Q3Base is a fork of Quake III Arena. It has the following advantages
over Quake III Arena itself:

- It uses SDL for establishing network connections. The client also uses
  it for loading textures (thus adding PNG support) and OpenGL
  rendering.
- It supports FreeBSD out of the box
- It hardcodes the shared object and datafile directories, thus removing
  the need of startup scripts

Q3Base is developed by the folks at Quakesrc.org.

WWW: http://www.quakesrc.org/