Do You Want to Play Some Puzzles?
March 15, 2015 5:57 PM Subscribe
Simon Tatham's Portable Puzzle Collection "I wrote this collection because I thought there should be more small desktop toys available: little games you can pop up in a window and play for two or three minutes while you take a break from whatever else you were doing. And I was also annoyed that every time I found a good game on (say) Unix, it wasn't available the next time I was sitting at a Windows machine, or vice versa; so I arranged that everything in my personal puzzle collection will happily run on both those platforms and more." In addition to the desktop implementations available at the website, the collection is also available on Android and iOS.
I'm guessing this might be a double, since I learned about the portable puzzle collection here on Metafilter, but maybe it was only ever in comments, not a stand alone FPP. It gets recommended a lot on AskMe.
Personally, I love me some Dominosa.
posted by jacquilynne at 6:28 PM on March 15, 2015
Personally, I love me some Dominosa.
posted by jacquilynne at 6:28 PM on March 15, 2015
Oh cool! This site is an old standby, but I didn't know that there was now an app. This'll be fun to toy around with while listening to podcasts. Thanks for the post!
posted by painquale at 6:28 PM on March 15, 2015
posted by painquale at 6:28 PM on March 15, 2015
This reminded me of how much I loved the 1978 board game Black Box. So I had to go to Ebay. You just cost me $20.
posted by frykitty at 6:29 PM on March 15, 2015 [2 favorites]
posted by frykitty at 6:29 PM on March 15, 2015 [2 favorites]
Thanks! Also, you are a jerk.
posted by Going To Maine at 6:31 PM on March 15, 2015 [1 favorite]
posted by Going To Maine at 6:31 PM on March 15, 2015 [1 favorite]
sgt-puzzles is fairly old, but the collection has been slowly growing. Since I last looked, he's added Tracks and Flood. It'd be nice if there was an announcements feed for new additions.
posted by pwnguin at 6:32 PM on March 15, 2015 [2 favorites]
posted by pwnguin at 6:32 PM on March 15, 2015 [2 favorites]
I mean, not really, but in a my-time-will-die-forever kind of way.
posted by Going To Maine at 6:32 PM on March 15, 2015
posted by Going To Maine at 6:32 PM on March 15, 2015
I'm guessing this might be a double, since I learned about the portable puzzle collection here on Metafilter, but maybe it was only ever in comments, not a stand alone FPP. It gets recommended a lot on AskMe.
Yep, only ever in comments. (It was once namechecked in an FPP about another game, though.) I found out about it through AskMe, too, and wanted to share with a wider audience.
posted by ocherdraco at 6:44 PM on March 15, 2015
Yep, only ever in comments. (It was once namechecked in an FPP about another game, though.) I found out about it through AskMe, too, and wanted to share with a wider audience.
posted by ocherdraco at 6:44 PM on March 15, 2015
I've had the apps (windows, android) for ages. I hadn't seen tracks was added -- neat. It's one of the first things I install on a device.
posted by jeather at 6:47 PM on March 15, 2015
posted by jeather at 6:47 PM on March 15, 2015
For those so inclined, the developer documentation is fascinating in its own right. The games are written in C using a custom cross-platform framework that provides things like undo support.
The most interesting section is probably "How to write a new puzzle".
posted by teraflop at 6:55 PM on March 15, 2015 [1 favorite]
The most interesting section is probably "How to write a new puzzle".
posted by teraflop at 6:55 PM on March 15, 2015 [1 favorite]
does anyone have a link to a discussion of strategy for Towers? I can't always solve the Extreme and Unreasonable ones.
posted by sineater at 7:02 PM on March 15, 2015
posted by sineater at 7:02 PM on March 15, 2015
"Unreasonable" means that there might be a unique solution, but there's no guarantee that deduction methods that will find it, leaving you to brute force every possible solution.
posted by pwnguin at 7:10 PM on March 15, 2015
posted by pwnguin at 7:10 PM on March 15, 2015
I've long considered making a post on this, it's terrific. Here's a few interesting facts:
That site above has Java and Javascript implementations of the puzzles, in addition to the native-compiled ones.
It's available for Android, for free with no ads! There is a $0.99 collection on iOS, "Puzzle Maniak," that seems to be a port, I don't know what arrangement they've made with Tatham, if any.
The Linux version of the collection accepts command line parameters. You can use those to actually create dynamically-generated PDFs of random puzzles, complete with answer keys, that you can print out and take on trips! I've read about how to do that before, and even done it, but for the life of me I can't find the info right now.
posted by JHarris at 8:00 PM on March 15, 2015 [1 favorite]
That site above has Java and Javascript implementations of the puzzles, in addition to the native-compiled ones.
It's available for Android, for free with no ads! There is a $0.99 collection on iOS, "Puzzle Maniak," that seems to be a port, I don't know what arrangement they've made with Tatham, if any.
The Linux version of the collection accepts command line parameters. You can use those to actually create dynamically-generated PDFs of random puzzles, complete with answer keys, that you can print out and take on trips! I've read about how to do that before, and even done it, but for the life of me I can't find the info right now.
posted by JHarris at 8:00 PM on March 15, 2015 [1 favorite]
I link to a free iOS version in the fpp that is referenced on the main puzzle collection page.
posted by ocherdraco at 8:37 PM on March 15, 2015 [1 favorite]
posted by ocherdraco at 8:37 PM on March 15, 2015 [1 favorite]
Ah! I missed those underlines at the end of the text. Very good -- get that, not the one I linked.
posted by JHarris at 9:09 PM on March 15, 2015
posted by JHarris at 9:09 PM on March 15, 2015
Galaxies is the one I keep coming back to. But they are all great. It's also fun spotting Souped Up Graphically Whizzy Versions Of The Same Game Presented As New...
posted by motty at 9:43 PM on March 15, 2015
posted by motty at 9:43 PM on March 15, 2015
Oof, the iPhone implementation is awful. Some games are nearly unplayable because of touch detection and the size of the tiny little dots you have to hit. Other games I can't even figure out how to interact with. The instructions are all just the instructions to the PC version (they tell you to right click, for instance). What a shame.
posted by painquale at 4:05 AM on March 16, 2015
posted by painquale at 4:05 AM on March 16, 2015
Net and Keen are the two web games that have eaten up the greatest amount of my free time over the last five years. Keen got me started on KenKen(link to Android app), which is a waaay better take on Sudoku.
posted by Mayor West at 5:04 AM on March 16, 2015
posted by Mayor West at 5:04 AM on March 16, 2015
Is this the same Simon Tatham who wrote PuTTY? Talk about containing multitudes.
posted by whuppy at 6:12 AM on March 16, 2015 [2 favorites]
posted by whuppy at 6:12 AM on March 16, 2015 [2 favorites]
I was about to say.. chiark.greenend.org.uk, I know that domain name. It's the guy who wrote PuTTY! But this collection seems to be a group effort, albeit headed up by Simon's platform. It's sort of a snapshot of the Time that Was, when hosting a few files on the web was hard and Linux desktop games were relevant. (There's PalmOS support, too!) The developer docs that teraflop linked are pretty amazing.
PuTTY is also pretty great. It's been very stable, had its first release in 18 months recently because of some relatively minor security problems.
posted by Nelson at 9:31 AM on March 16, 2015 [2 favorites]
PuTTY is also pretty great. It's been very stable, had its first release in 18 months recently because of some relatively minor security problems.
posted by Nelson at 9:31 AM on March 16, 2015 [2 favorites]
That site above has Java and Javascript implementations of the puzzles
I wasn't aware of the Javascript versions: a good alternative to installing the Windows binaries (ugh! and why is it one-binary-per-game for Windows vs. one-binary-with-all-the games for the other platforms?) or firing up the Java applets (double ugh!).
posted by We had a deal, Kyle at 6:16 PM on March 16, 2015
I wasn't aware of the Javascript versions: a good alternative to installing the Windows binaries (ugh! and why is it one-binary-per-game for Windows vs. one-binary-with-all-the games for the other platforms?) or firing up the Java applets (double ugh!).
posted by We had a deal, Kyle at 6:16 PM on March 16, 2015
There's an installer for every game for Windows if you scroll a bit more.
posted by jeather at 6:54 PM on March 16, 2015
posted by jeather at 6:54 PM on March 16, 2015
Excellent! Getting sucked into 'Bridges' at the moment ...
posted by carter at 8:04 PM on March 16, 2015
posted by carter at 8:04 PM on March 16, 2015
Personally, I love me some Dominosa.
How do you get started on solving a Dominosa board? It was more obvious how to get started on solving in Loopy: 0 squares are obvious, and the corners also provide starting constraints.
(In a lot of these I'd kill for a Hint button: show me one step towards the solution, rather than the Solve button which does all of it at once.)
posted by We had a deal, Kyle at 3:32 PM on March 17, 2015 [1 favorite]
How do you get started on solving a Dominosa board? It was more obvious how to get started on solving in Loopy: 0 squares are obvious, and the corners also provide starting constraints.
(In a lot of these I'd kill for a Hint button: show me one step towards the solution, rather than the Solve button which does all of it at once.)
posted by We had a deal, Kyle at 3:32 PM on March 17, 2015 [1 favorite]
I've played a lot of Dominosa for years and can answer that one.
It helps, when starting doing Dominosa puzzles, to write out on paper all the dominos, from 0-0 to whatever-whatever, usually 5-5 I suppose. After your first puzzle you'll probably find this step is unnecessary, but it can help you to see implications.
Let's call the highest number on the board N. Remember, each domino is used exactly once. You see the numbers, but not the borders between them.
There are exactly N+2 of each digit on the board. Further, there will always be at least one double of each digit. These are the best place to start. Scan the board and look for pairs of numbers. Best case is single pairs, places where there's only one place in the entire puzzle there's a puzzle. In those places you can be certain that's where the domino goes, can place it on the board, and cross it off your list.
Sometimes this will get you started: any place with a free number surrounded by other dominos or puzzle edges on three sizes is a place where you can put a new domino, because you can't have free numbers. Then you can cross it off the list. Every time you place a domino like that, you rule out all the potential places on the board that connect those two numbers, because there's only one of each number combination. The game will help you with this: if you place a domino somewhere where there's a match elsewhere, it'll show in red. And you can take advantage of this, you can right-click/click twice on a spot to put a border line there, to mark it as impossible.
Usually this isn't enough to solve the puzzle by itself. From there, there are two major steps to solving the puzzle.
STEP ONE: Ruling out impossible places, placing new dominos based on those places, and going back and forth, iteratively.
There are some tricks you can do to rule some places out. For example, let's look at this N=3 puzzle:
These kinds of tactics will often get you some distance, but sometimes they stall out. In that case, one thing to try is going over the puzzle and finding places single pairs of numbers, pairs that aren't duplicated elsewhere. This is time-consuming, but not too difficult with practice. Start with 0-1 (you've already done doubles) and look if there's only one place where there's that combination in the puzzle. If there is, you can mark that domino, and maybe others. If not, try 0-2, then 0-3, and so on. When you're done with 0, you can do 1-2, then 1-3, 1-4, 1-5. Then, 2-3, 2-4, 2-5. Then, 3-4, 3-5, then, 4-5. Note, after you've done one number this way, the others get easier, because you've already checked some of them. So while it's laborious, after doing doubles, there's only 15 such combinations to check on an N=5 puzzle.
STEP TWO: Sometimes tricks and that, and the places they reveal that demand specific domino placement, are enough to complete the puzzle. But sometimes it's not. All the remaining free pairs have multiple possibilities. Then you must play trial and error: picking arbitrary dominos and seeing if they present contradictions, then undoing back to where you picked. In these cases, it's best if you pick dominos that don't work out: you aren't looking for spots that work, but those that don't, because you can then place blocking lines there, and those might give you more guarenteed placements. Or alternatively, you might accidentally pick an arbitrary spot that, once you work out the implications, solves the puzzle. A lot of these puzzles, on the harder difficulties, resolve down to trial and error. This is not a flaw: even hard Sudoku puzzles to this.
I actually have these kinds of solving methods tricks worked up for several other puzzles, especially Slant and Loopy, which I've spent a lot of time with. I think part of the fun of doing a new puzzle is in devising these solving algorithms, but if someone wants to hear, I'm happy to share.
By the way, as the documentation for most of these games notes, a lot of these puzzles have their origin in the pages of the Japanese puzzle magazine Nikoli. If you like them, but don't speak Japanese, I've noticed sometimes GAMES/World of Puzzles Magazine publishes Nikoli puzzles.
posted by JHarris at 4:13 PM on March 17, 2015 [2 favorites]
It helps, when starting doing Dominosa puzzles, to write out on paper all the dominos, from 0-0 to whatever-whatever, usually 5-5 I suppose. After your first puzzle you'll probably find this step is unnecessary, but it can help you to see implications.
Let's call the highest number on the board N. Remember, each domino is used exactly once. You see the numbers, but not the borders between them.
There are exactly N+2 of each digit on the board. Further, there will always be at least one double of each digit. These are the best place to start. Scan the board and look for pairs of numbers. Best case is single pairs, places where there's only one place in the entire puzzle there's a puzzle. In those places you can be certain that's where the domino goes, can place it on the board, and cross it off your list.
Sometimes this will get you started: any place with a free number surrounded by other dominos or puzzle edges on three sizes is a place where you can put a new domino, because you can't have free numbers. Then you can cross it off the list. Every time you place a domino like that, you rule out all the potential places on the board that connect those two numbers, because there's only one of each number combination. The game will help you with this: if you place a domino somewhere where there's a match elsewhere, it'll show in red. And you can take advantage of this, you can right-click/click twice on a spot to put a border line there, to mark it as impossible.
Usually this isn't enough to solve the puzzle by itself. From there, there are two major steps to solving the puzzle.
STEP ONE: Ruling out impossible places, placing new dominos based on those places, and going back and forth, iteratively.
There are some tricks you can do to rule some places out. For example, let's look at this N=3 puzzle:
0 3 1 1 0 3 0 1 2 2 1 0 2 3 3 2 0 2 1 3This puzzle has no singleton doubles in it. But we can still mark a few places. That place with the vertical line of zeros for instance. Those are the only places with double 0s in the puzzle, and they both share a 0. So, the double-0 must contain that zero. That means that zero must connect either up or down, meaning we can place a couple of lines in the puzzle. We can use the same logic on the "bend" of threes in the lower-right corner, and the bend of 1s in top middle. After ruling out those possibilities, we have:
0 3|1 1 0
3 0 1 2 2
-
1|0|2 3 3
2 0 2 1 3Now note, in the upper-left corner, I've boldfaced a 2x2 square of numbers. These are the only spots with 0-3 in the puzzle. Before you ruled out those places, it wasn't obvious which of these four possibilities 0-3 could be. But now we know, because there's only one 0-3 domino, that it has to be one of the ones that connects to the second 3 in the first row; if it was the other 3, then there would have to be a duplicate. That lets us draw two additional lines:
0 3|1 1 0
-
3|0 1 2 2
-
1|0|2 3 3
2 0 2 1 3From this point solving this puzzle is pretty easy, see if you can take it from there.These kinds of tactics will often get you some distance, but sometimes they stall out. In that case, one thing to try is going over the puzzle and finding places single pairs of numbers, pairs that aren't duplicated elsewhere. This is time-consuming, but not too difficult with practice. Start with 0-1 (you've already done doubles) and look if there's only one place where there's that combination in the puzzle. If there is, you can mark that domino, and maybe others. If not, try 0-2, then 0-3, and so on. When you're done with 0, you can do 1-2, then 1-3, 1-4, 1-5. Then, 2-3, 2-4, 2-5. Then, 3-4, 3-5, then, 4-5. Note, after you've done one number this way, the others get easier, because you've already checked some of them. So while it's laborious, after doing doubles, there's only 15 such combinations to check on an N=5 puzzle.
STEP TWO: Sometimes tricks and that, and the places they reveal that demand specific domino placement, are enough to complete the puzzle. But sometimes it's not. All the remaining free pairs have multiple possibilities. Then you must play trial and error: picking arbitrary dominos and seeing if they present contradictions, then undoing back to where you picked. In these cases, it's best if you pick dominos that don't work out: you aren't looking for spots that work, but those that don't, because you can then place blocking lines there, and those might give you more guarenteed placements. Or alternatively, you might accidentally pick an arbitrary spot that, once you work out the implications, solves the puzzle. A lot of these puzzles, on the harder difficulties, resolve down to trial and error. This is not a flaw: even hard Sudoku puzzles to this.
I actually have these kinds of solving methods tricks worked up for several other puzzles, especially Slant and Loopy, which I've spent a lot of time with. I think part of the fun of doing a new puzzle is in devising these solving algorithms, but if someone wants to hear, I'm happy to share.
By the way, as the documentation for most of these games notes, a lot of these puzzles have their origin in the pages of the Japanese puzzle magazine Nikoli. If you like them, but don't speak Japanese, I've noticed sometimes GAMES/World of Puzzles Magazine publishes Nikoli puzzles.
posted by JHarris at 4:13 PM on March 17, 2015 [2 favorites]
Dominosa is primarily about hunting for combinations that occur only once.
I usually progress through the puzzle this way:
-- Look at the four corners to see if any of them have the same number appearing in both directions, like this:
5 4
4
If so, look at all the other 5s and mark any 5 4 combos as not possible dominos.
-- Scan the board for all the doubles and see if any of those only occur once on the board. Doubles aren't particularly significant or significantly more likely to only occur once, they are just easier to see. While you're doing this, if you run across any numbers where the possible doubles are in different directions off a single tile, you can at least mark the other edges of that tile as not possible dominos, as well.
-- Look at individual numbers, starting with any numbers where you found a unique double (because if you found and marked off the double-threes, there are now fewer threes to look through) and see if there are any combos that are unique on the board. So, check all the 3s and see how many 3 0 combinations there are, how many 3 combinations there are, etc.
-- Look at any places where a tile pivots only 2 other tiles and treat it like the corners from step 1.
-- Look for any places where you have a set of tiles blocked off by dominos or not-possible marks with only one outlet and count the enclosed tiles to see whether that one tile belongs in or out of the set and mark it appropriately.
-- Look for number combinations that repeat in such a way that you know that a specific set of pivots have to contain those combinations. So, if you have a 6 tile in one spot where the only choices look like this:
6 3
4
And another tile in another spot where a 6 also only has 3s and 4s, say:
4
6 4
3
You know that those two 6s are going to contain the 6 3 and 6 4 combination, and any other 6 that has a 3 or a 4 next to it can have that marked as not possible. It is relatively unusual (maybe 20% of the time) to actually need to do this to solve puzzles, but sometimes if you don't get many uniques, it'll need to get this specific.
There are some other tiny little tells I watch for that let me mark things as impossible, but those are the basic ones.
posted by jacquilynne at 4:24 PM on March 17, 2015 [1 favorite]
I usually progress through the puzzle this way:
-- Look at the four corners to see if any of them have the same number appearing in both directions, like this:
5 4
4
If so, look at all the other 5s and mark any 5 4 combos as not possible dominos.
-- Scan the board for all the doubles and see if any of those only occur once on the board. Doubles aren't particularly significant or significantly more likely to only occur once, they are just easier to see. While you're doing this, if you run across any numbers where the possible doubles are in different directions off a single tile, you can at least mark the other edges of that tile as not possible dominos, as well.
-- Look at individual numbers, starting with any numbers where you found a unique double (because if you found and marked off the double-threes, there are now fewer threes to look through) and see if there are any combos that are unique on the board. So, check all the 3s and see how many 3 0 combinations there are, how many 3 combinations there are, etc.
-- Look at any places where a tile pivots only 2 other tiles and treat it like the corners from step 1.
-- Look for any places where you have a set of tiles blocked off by dominos or not-possible marks with only one outlet and count the enclosed tiles to see whether that one tile belongs in or out of the set and mark it appropriately.
-- Look for number combinations that repeat in such a way that you know that a specific set of pivots have to contain those combinations. So, if you have a 6 tile in one spot where the only choices look like this:
6 3
4
And another tile in another spot where a 6 also only has 3s and 4s, say:
4
6 4
3
You know that those two 6s are going to contain the 6 3 and 6 4 combination, and any other 6 that has a 3 or a 4 next to it can have that marked as not possible. It is relatively unusual (maybe 20% of the time) to actually need to do this to solve puzzles, but sometimes if you don't get many uniques, it'll need to get this specific.
There are some other tiny little tells I watch for that let me mark things as impossible, but those are the basic ones.
posted by jacquilynne at 4:24 PM on March 17, 2015 [1 favorite]
Then you must play trial and error: picking arbitrary dominos and seeing if they present contradictions, then undoing back to where you picked.
Sometimes this may be the fastest option, but as far as I can tell, it is never actually necessary. In years of playing Dominosa, I have never run across a puzzle I couldn't logic through without trial and error. If there are cases where you can't, they are rare beasts like the unsolvable Free Cell deals.
posted by jacquilynne at 4:28 PM on March 17, 2015
Sometimes this may be the fastest option, but as far as I can tell, it is never actually necessary. In years of playing Dominosa, I have never run across a puzzle I couldn't logic through without trial and error. If there are cases where you can't, they are rare beasts like the unsolvable Free Cell deals.
posted by jacquilynne at 4:28 PM on March 17, 2015
Aw, you two are the best. I shall give it another go.
posted by We had a deal, Kyle at 4:45 PM on March 17, 2015
posted by We had a deal, Kyle at 4:45 PM on March 17, 2015
I want to love dominosa. It's just the right level of deduction and mindlessness that suits a morning commute, but the lack of a "these are the dominoes left" tracker drives me batty.
(The android app is my constant commute companion. Since the pre android 2.0 days I'm pretty sure.)
posted by aspo at 5:22 PM on March 17, 2015
(The android app is my constant commute companion. Since the pre android 2.0 days I'm pretty sure.)
posted by aspo at 5:22 PM on March 17, 2015
I can personally vouch it's sometimes necessary, jaquilynne. They are not nearly as rare as impossible Freecell deals.
In my description, I'm sorry for a few typos, I was writing it fairly quickly and focusing on getting the pre tags right. plus was in a great hurry, but I trust you can piece together my meaning. Particularly, "places where there's only one place in the puzzle where there's a puzzle." God,I assure you I can write.
posted by JHarris at 7:00 PM on March 17, 2015 [1 favorite]
In my description, I'm sorry for a few typos, I was writing it fairly quickly and focusing on getting the pre tags right. plus was in a great hurry, but I trust you can piece together my meaning. Particularly, "places where there's only one place in the puzzle where there's a puzzle." God,I assure you I can write.
posted by JHarris at 7:00 PM on March 17, 2015 [1 favorite]
Hmm, I just can't fit my brain around Dominosa: it still feels too much like a word-search, hasn't flipped over into pattern-recognition and induction yet.
Loopy though: yeah.
posted by We had a deal, Kyle at 3:35 PM on March 20, 2015
Loopy though: yeah.
posted by We had a deal, Kyle at 3:35 PM on March 20, 2015
Although they're not free, Everett Kaser makes some pretty similar (and very good) logic games.
posted by jeather at 4:56 PM on March 20, 2015
posted by jeather at 4:56 PM on March 20, 2015
Sometimes the sgt-puzzles generators are not very good -- I recall Singles being easily defeated, but cannot recall why. Perhaps it has been fixed since I gave up on that one.
Still, if you want something more challenging and hand generated, the US Puzzle Championship provides a backlog of practice and actual tests used to select the US delegation to the World Puzzle Championship (artist's rendition). You end up with a set of PDFs of some very challenging and often unique spins on puzzles.
The USPC site is somewhat clunky because they appear to have designed to minimize and unfair advantage -- they distribute encrypted versions of the PDF that folks can download at their leisure and release the decryption key later. I don't think the passwords are typically very secure, so I've often wondered if anyone's bothered to try and crack the password to get a head start, like kind of Chunin Exam.
And it's not like people don't write software to help them win; since unlike sgt-puzzles, there's no software defining what deduction markings you can make, Denis Auroux wrote Xournal to help him solve these sorts of puzzles at a computer. It's chiefly a note taking & pdf annotation tool, but very handy for scribbling, and undoing scribbles, and saving them for later.
posted by pwnguin at 10:33 PM on March 20, 2015 [2 favorites]
Still, if you want something more challenging and hand generated, the US Puzzle Championship provides a backlog of practice and actual tests used to select the US delegation to the World Puzzle Championship (artist's rendition). You end up with a set of PDFs of some very challenging and often unique spins on puzzles.
The USPC site is somewhat clunky because they appear to have designed to minimize and unfair advantage -- they distribute encrypted versions of the PDF that folks can download at their leisure and release the decryption key later. I don't think the passwords are typically very secure, so I've often wondered if anyone's bothered to try and crack the password to get a head start, like kind of Chunin Exam.
And it's not like people don't write software to help them win; since unlike sgt-puzzles, there's no software defining what deduction markings you can make, Denis Auroux wrote Xournal to help him solve these sorts of puzzles at a computer. It's chiefly a note taking & pdf annotation tool, but very handy for scribbling, and undoing scribbles, and saving them for later.
posted by pwnguin at 10:33 PM on March 20, 2015 [2 favorites]
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