A unix chess program, which learns as of version 3.0. It is not as strong as crafty, but its evaluation learning feature is the most impressive around. Source for various versions is available in this ftp directory . The program has two forms of learning. Opening book learning remembers losing moves and stores them into the hash table before a search begins.
Temporal difference learning updates the evaluation function weights.
You can program new evaluation function components, and KnightCap will learn their weights. Pellen A weak neural-network chess program for Windows. There's a short discussion of the program, user documentation, and an executable to download. You train up the network with master games or whatever you want, and play against the resulting program. I think it looks like a fun way to play around with neural networks.