Arasan is a chess program for Windows, Linux and Mac OS. It is copyrighted, but allows free distribution, with some restrictions.
The latest version is Arasan 13.4, released in December, 2011.
Arasan has both a native user interface (for Windows only) and a console-based chess engine for use with Winboard or xboard. Arasan also works with Arena, another free chess interface, and with UCI-compatible programs like Shredder.
Arasan includes an opening "book" with over 200,000 moves.