Tim Mann is the author of Winboard (a free graphical interface to allow computer programs to play against each other), also information on: GNU Chess, XBoard, WinBoard, Crafty, Internet Chess Servers, Zippy, Chess Web Sites, Chess FTP Sites, and more.
This is probably the most famous tournament for chess engines.
FICS is a Free Internet Chess Server.
Another Free Internet Chess Server with a Java interface. Not so many opponents, but at least they’re all human!.
The home page of DarkThought. Some interesting topics on how DarkThought plays chess.
Home page of the Beowulf Computer Chess Engine. Contains information on chess programming theory.