Source: TweakGuides
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Originally called S.T.A.L.K.E.R. - Oblivion Lost, S.T.A.L.K.E.R. (hereby referred to without the periods) was announced as far back as 2001 and was due for release in mid 2003. As this screenshot gallery from 2003 shows, the game was quite well-developed, and ahead of its time. It also featured a futuristic theme complete with robots and advanced weaponry, but the graphics and game world was quite similar in appearance to that we see in STALKER today. However somewhere along the way, the game required redevelopment to such a degree that it took another four years past its original due date for it to come to fruition. Fortunately, despite the many doubters and claims that the game was 'vaporware', STALKER: Shadow of Chernobyl has finally been released.