OpenArena is a free/open source 3D computer game that belongs to the "first-person shooter" genre. OpenArena had its first public test release on August 19 2005, the day after the Quake 3 engine GPL source code release and also the last day of Quake Expo 2005.
OpenArena is developed mainly using free/open source - e.g. its game engine is id Software's GNU GPL Quake 3 engine. OpenArena is entirely free as in speech (both engine, gamecode and data) - pure Open Content
It is still in very early development. In addition, a "missionpack" addon is planned, to take advantage of the also GPL'd Quake III: Team Arena source code.