"In an almost unheard-of move, S.T.A.L.K.E.R.: Shadow of Chernboyl developer GSC Game World has released an early build of its 2007 post-apocalyptic shooter, allowing fans a peek at cut levels and unfinished features.GSC Releases Early S.T.A.L.K.E.R. Build from 2004
The playable build--dated October 18, 2004 and called the "xrCore build 1935"--is available from a number of sources linked from the GSC-created forum thread.
Several levels unused levels including Dead City, Swamp and Generators are explorable in the build."