Chessmaster - Chess for mobile phones [Commercial]
ChessWorks - Multiplayer chess game that is playable over the internet or a LAN. [Macintosh/Windows]
Ghost - Ghost by Philipp Claßen. Ghost is an amateur chess program written in C++. Runs on Windows and Linux.
Kuro5hin - Assembly program by David Horne, which is run on the ZX81 with just 1k of memory.
