Portal 2 is a first-person puzzle-platform video game developed and published by Valve Corporation. It is the sequel to Portal and was released on April 18, 2011 for Microsoft Windows, Mac OS X, PlayStation 3, and Xbox 360. The retail versions of the game are distributed by Electronic Arts, while digital distribution of the Windows and OS X versions is handled by Valve's content delivery service Steam. Portal 2 was announced on March 5, 2010, following a week-long alternate reality game based on new patches to the original game.
The sequel's release on Steam was preceded by a second multi-week alternate reality game, the Potato Sack, involving 13 independently-developed titles which culminated in a distributed computing spoof to release Portal 2 several hours early.