Urban Terror
Urban Terror started as a realism based "total conversion" mod for Quake III Arena. Nowadays, Urban Terror is played using the free, stand-alone, ioquake3 engine modified, which doesn't require Quake III Arena, in addition to being an add-on to id Software's Quake III Arena.
Urban Terror is 100% free. It is a condition of the End User Licensing Agreement (EULA) when creating a mod that it not to be released for commercial retail. That means the team Frozen Sand who created Urban Terror is doing it for free. If you purchased Urban Terror, then some unscrupulous individual may have ripped you off. You should immediately report them to id Software or Frozen Sand.
Download data files from the following link: http://vlaai.snt.utwente.nl/pub/games/urbanterror/full_install/linux_or_mac/UrbanTerror411.zip