Valve Corporation is an American videogame developer, engine developer, and digital distributor originally founded in Kirkland, Washington but now based in Bellevue, Washington. It was developed for Microsoft Windows, Mac OS X, Xbox 360, and PlayStation 3. Its engine, Source, is the basis for several games released both by Valve and other videogame developers. It created Steam in 2002 to distribute and support multiplayer for its games, and has since expanded Steam to many other developers. Notable franchises include Half-Life, Left 4 Dead, Portal, Team Fortress, and Portal 2. Valve Corporation is also the subject of the phrase "Valve Time," which indicates publishing delays.