"GNU Chess lets most modern computers play a full game of chess. It has a plain terminal interface but supports visual interfaces such as X-Windows "xboard" and Windows-for-PC "winboard" as well as a full 3-dimensional wooden chess-board protocol for
the Novag Chess board enabling one to be relatively free of the computer itself."
(From GNU home page)
GNU Chess is a chess program - while not as cool as some big commercial chess programs, or not as effective as certain IBM things, it's nevertheless a game that at least beats me (as if that'd prove anything =)