xfire is a foaf-based social software that allow you to :

-see WHEN your friends are playing online games - See WHAT game they are playing - See WHERE they are playing - JOIN their game with just one click! - unlike existing Instant Messengers, Xfire lets you receive IM's without disrupting your game!

Games supported by Xfire currently include: America's Army, Battlefield 1942, Counter-Strike, EverQuest, Halo, Lineage, Quake III, Starcraft, Unreal Tournament 2003, Warcraft III, Call of Duty, Final Fantasy XI, and over 50 m