Portal 2 is a first-person puzzle-platform video game developed by Valve Corporation. It is the sequel to the 2007 video game Portal and was announced on March 5, 2010, following a week-long alternate reality game based on new patches to the original game. Though initially slated for release in the last quarter of 2010, the game was postponed to the week of April 18, 2011. The game was released by Valve through Steam for Microsoft Windows and Mac OS X, while the PlayStation 3, Xbox 360 and retail Windows/OS X versions of the game are distributed by Electronic Arts. The game's release on Steam was preceded by a second multi-week alternate reality game, the Potato Sack, involving 13 independently-developed titles, culminating in a distributed computing spoof to release Portal 2 several hours early.
