Crafty – a free, open-source computer chess program developed by UAB (University of Alabama at Birmingham) Dr. Robert M. (Bob) Hyatt.
Crafty is the strong chess program played on ICC. It uses all of the search algorithms you have probably read about and performs better than gnu-chess in most positions. It has a reasonable set of features to use, and offers a great starting point to try your own new search extensions.
Crafty can be compiled and executed from a terminal window on a Macintosh, Windows or Linux computer. Crafty can also be run with a GUI interface such as Winboard (Windows) or Xboard (Linux).
Valters Baumanis has written his own Crafty Chess interface that be downloaded here.