Games:

FPS Garry's Mod gamemode. Large group of players of which some are "Traitors" who must kill all non-Traitors to win. Other players do not know who is a Traitor and who is not, but can piece together clues or catch them red handed. Developed mostly between September 2009 and March 2010.

Zombie Master
FPS/RTS Source engine mod. There are zombies in it here and there. One player controls them RTS-style while the others fend them off and complete objectives as FPS players. Development started in 2005, first public release in 2007, last release in 2009.