Since it is so hard to find a truly Open Source FPS, here's a list which should clear things up:

Real Open Source ShootersEdit

• FreeDoom - everything modified BSD.
• Nexuiz - everything GPL (However, the tradmark and engine were relicensed for commercial use)
• Xonotic - Everything GPL (Based on Nexuiz source code after reliscencing )
• Open Quartz - everything GPL.
• Red Eclipse - Based off Cube 2 engine, under zlib, content under Creative Commons Attribution-ShareAlike.
• Tremulous - engine GPL, content mostly Creative Commons Attribution-ShareAlike.
• TUER - code source under GPL, artworks without licence

OSShooters somewhere betweenEdit

• Cube - Partly open source engine (network code is not, neither does the contents)

OpenSourceEngine but closed contentEdit

These games use an Open Source game engine and/or gamecode, but the content is only free as in beer, not freedom in the true sense of the word; they are effectively more like freeware games.

• AlienArena
• Argonium
• AssaultCube
• Revolution
• Sauerbraten aka Cube2
• Warsow
• World of Padman
• Wolfenstein: Enemy Territory
• Smokin' Guns

Freeware (Non Open Source)Edit

We'll just list them, as they are not important for our project:

• Americas Army

• F.E.A.R Combat

• War Rock

LinksEdit

• http://www.quakesrc.org/forums/viewtopic.php?t=4485
• http://en.wikipedia.org/wiki/List_of_free_first_person_shooters