I've been toying with the concept of very simple, distilled strategy games that don't take long to play, but involve some brainwork on some level. I was already thinking about putting a game of some sort on a very small (maybe 5x5) board, and then I stumbled across a description of Quadpawn, an old C-64 game. Each side has four pawns on a 4x4 board, and the objective is to either get a piece to the other side of the board, or prevent the other player from being able to move. The game concept is also described on algorithmist.com.

Anyway, here's a version in Flash. The source code is available as well.

The game is simple, and once you get the hang of it, it's not hard to win most of the time, but it stayed enjoyable the whole time I was playing it.

The sourcecode is pure AS3, so you don't need Flash to compile it. Among other things, it has a pretty clean implementation of the minimax algorithm, something that is reasonably hard to come across.