Phutball (Rules, Java Applet), aka Philosophers' Football or ConwayGo is a deceptively simple 2-player game you can play on a Go board, or any rectangular grid. (It may be simple, but finding the right move is [PDF] NP Complete.)
posted by Wolfdog on Aug 2, 2005 - 7 comments

Beyond Life [Java]. Mirek's Cellebration is an beautiful applet for exploring all sorts of cellular automata. Source code and standalone version also available.
posted by Wolfdog on Jan 4, 2005 - 7 comments

Flash and Java Enigma machines. And, if you're burdened with free time, an excellent text adventure in which Enigma-deciphering plays a crucial role.
posted by Wolfdog on Dec 28, 2004 - 12 comments

Copycat [Java] - long available only in its rickety original LISP source - is now an interactive applet. You can propose analogy puzzles based on strings of letters and watch Copycat build up and tear down models of the problem until it finds a solution it's happy with. It will explain its reasoning, and, since stochastic elements are inolved, can come up with alternate solutions upon rerun. Tutorial for the applet here; or, explore MetaCat, the next generation follow-up.
posted by Wolfdog on Dec 2, 2004 - 6 comments