Valve Corporation (also known as Valve Software, commonly referred to as Valve) is an American video game developer and digital distribution company headquartered in Bellevue, Washington, United States. Its Luxembourg-based business office subsidiary for European regions, Valve S.a.r.l., was opened in 2012. Founded in 1996 as Valve L.L.C. by former Microsoft employees Gabe Newell and Mike Harrington, the company has developed the critically acclaimed Half-Life, Counter-Strike, Portal, Day of Defeat, Team Fortress, Left 4 Dead video game series, alongside Dota 2. It also developed and maintains Source on which most of its games run, and the software distribution platform Steam, which has led to the Steam Machine, a line of pre-built gaming computers running SteamOS.