Fav Open Source FPS game

[Buds Bundy]

So list your favourite Open Source First Person Shooter(s).

Xontoic from http://www.xonotic.org really after playing it there's not going back to anything else. Oh and I also run several Xontotic servers so I am biased

 

[Agracan]

Perhaps not open source but free: Americas Army. Especially the new Proving Grounds