Saw this on stumbleupon. Thought it looked pretty cool. Players are divided into two teams - snipers and spies. The sniper's job is to observe a party, single out the enemy spy, and take him out using one shot. The spy has to maneuver around the party, completing secret objectives while avoiding detection. It's still a long way off from completion, but I think people might be able to purchase a beta version.
http://www.spyparty.com/
http://kotaku.com/5500968/the-next-smart-video-game-only-lets-you-kill-once
http://www.spyparty.com/
http://kotaku.com/5500968/the-next-smart-video-game-only-lets-you-kill-once