Thief is a free chess client to play on chess servers like FICS: http://www.freechess.org It supports regular chess and all variants played. It is the best client for playing Bughouse, a special team-chess game (for more info see http://www.bughouse.
I like it. It could be rewrite with Qt4 to run in others OS (Windows, Linux e Mac OS X) with the same core code. I'm using. It's cool!!! Thank you!