Open source remakes of games you're still loving
Some FPS additions:AlienArena - like UT, Q3A. Graphically impressive, seems to be actively developed.http://red.planetarena.org/Nexuiz - like UT, Q3A.  Also decent graphics, seems devs are working on a commercial sequel now, so the last major version was in 2009.http://sourceforge.net/projects/nexuiz/OpenArena - like Q3A. Seems to be an attempt to recreate Quake 3 Team Arena from the GPL source with new content, some graphical improvements.http://www.openarena.ws/Tremulous - like Gloom, Natural Selection etc.  Sci-fi FPS/RTS hybrid.http://tremulous.net/Urban Terror - like Counter-Strike, but a little more arcade-style.EDIT: free but not yet open sourcehttp://www.urbanterror.info/