Portal 2 was released for a platform.
Portal 2 . Before the game 's release on Steam , the company released the Potato Sack , a second multi-week alternate reality game , involving 13 independently developed titles which culminated in a distributed computing spoof to release Portal 2 several hours early . Steam is a digital distribution platform developed by Valve Corporation , which offers digital rights management ( DRM ) , multiplayer gaming , video streaming and social networking services .