Left 4 Dead 2, is set to launch on PC, Mac and Xbox 360 on July 24. Cold Stream includes a fan-made campaign, and ports of Left 4 Dead's Death Toll, Dead Air, Blood Harvest and Crash Course levels.
Cold Stream first entered beta in March 2011 and is still open for PC and Mac on Steam, making this launch more of an official, polishing update for those platforms. Valve initially said Cold Stream would launch "some time after Portal 2," and really, it's not as if they were wrong about that one. Clever, Valve. Clever.