Simon Tatham's Portable Puzzle Collection

Here is an excerpt from Simon Tatham's Portable Puzzle Collection's description on the game's official website:

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.

When I find (or perhaps invent) further puzzle games that I like, they'll be added to this collection and will immediately be available on both platforms. And if anyone feels like writing any other front ends for platforms I don't support (which people already have) then all the games in this framework will immediately become available on another platform as well.

The actual games in this collection were mostly not my invention; they are re-implementations of existing game concepts within my portable puzzle framework. I do not claim credit, in general, for inventing the rules of any of these puzzles. (I don't even claim authorship of all the code; some of the puzzles below have been submitted by other authors.)