S.T.A.L.K.E.R.: Clear Sky

S.T.A.L.K.E.R.: Clear Sky is a first-person shooter game in the S.T.A.L.K.E.R. series. It is the prequel to S.T.A.L.K.E.R.: Shadow of Chernobyl. It was developed by Ukranian developer GSC Game World, and was first released in Russia on the 22nd August, 2008. The game originally had DRM to restrict usage to 5 machines. This restriction was removed in later versions of the game.