Series: NetHack
Play free games part of the "NetHack" series

UnNetHack
RPG / roguelike
Windows, Linux, Mac OSXUnNetHack team

NetHack: Falcon's Eye
RPG / roguelike
Windows, DOS, LinuxJaakko Peltonen

Hack
RPG / roguelike
Windows, DOS, Linux, Free BSD, UNIXJay Fenlason