This project, icculus.org/quake3 (sometimes referred to ioquake3, or ioq3 for
short) aims to build upon id Software's Quake 3 source code release. The
source code was released on August 20, 2005 under the GPL. Since then, we have
been cleaning up, fixing bugs, and adding features. Our permanent goal is to
create the open source Quake 3 distribution upon which people base their games
and projects. We also seek to have the perfect version of the engine for
playing Quake 3: Arena, Team Arena, and all popular mods. This distribution of
the engine has been ported to many new platforms and has had a slew of new
features added, along with massive bug extermination.

WWW: http://ioquake3.org/