Valve, creators of best-selling game franchises (such as Counter-Strike, Half-Life, Left 4 Dead, Portal, and Team Fortress) and leading technologies (such as Steam and Source), today introduced support for Free to Play (F2P) Games on Steam with the launch of five F2P games.

Available immediately, the launch titles are Spiral Knights, Forsaken Worlds, Champions Online: Free for All, Global Agenda: Free Agent, and Alliance of Valliant Arms (AVA).

Beginning tomorrow (Weds) with Spiral Knights and concluding Sunday with AVA, each of the five launch titles will offer exclusive in-game content to those who try the "F2P game of the day" on Steam. In game transactions in all of the titles will be supported by Steam's micro-transaction backend system that is available to Steamworks partners and currently used in Valve's Team Fortress 2.