chess.el is an Emacs Lisp library and several clients on top of the underlying library functionality for performing various activities related to the game of chess. You can play against an external chess program such as gnuchess, crafty, phalanx or sjeng. All of them are publically available, and chess.el will automatically detect which one you have installed, provided they have standard executable program names, and are in a located in a directory which is part of the PATH. See the customisable variable `chess-default-engine'. You can also play against another human or computer over the internet (through a direct Emacs-to-Emacs connection, or on one of the Internet Chess Servers like freechess.org or chessclub.com), or even against a very simple chess thinking module implemented in pure Emacs Lisp. chess.el also provides a mode for editing Portable Game Notation (PGN) files.