I couldn't find anything on macosxhints.com, so I thought I would post this. In Terminal, navigate into the Chess.app package:
$ cd /Applications/Chess.app/Contents/Resources/
You'll find that Chess.app is based on the free chess program Sjeng (version 11.2). So you can play it in the Terminal, if you wish. Just type ./sjeng (link to it for easier access), and have fun!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060406155023469