[EvilPopsicleDog]

Yes, but the possible input to a chess game is strictly limited - one player cannot just change the way a piece moves or introduce a new piece, and thus, it is not taken into account in any strategy. These sorts things must be taken into account when programming.

[zwischenzug]

This is how a chess player thinks. "Jesus, why did she play that? She must have seen something I've missed. Shit, if I had more time I'd be able to figure it out. Damnit, I'll just move my knight back, that way my king'll be safer. I'm sure there's a better move but I can't find it now, and I think my ass went to sleep."

Change a few words, and it's pretty much a typical thought process when coding for me.

[bzalasky]

Bughouse chess might fit the bill in this case. If you're not familiar, there are two boards with four players, with teammates playing opposite colors on each board. A captured piece on one board can be held in reserve by the teammate and played on any subsequent turn on any open square on the other board.