S.T.A.L.K.E.R. is a FPS developed by the Ukrainian developer GSC Game World, published for PC in 2007. As we can read in Wikipedia, the game was first announced in November 2001 as “S.T.A.L.K.E.R. Oblivion Lost” and had its release date, originally in 2003, pushed back several times. Meanwhile hundreds of screenshots of the game had been released, as well as a dozen preview video clips, due to years of delays some considered S.T.A.L.K.E.R. to be vaporware.
In late December 2003, a pre-alpha build of the game was leaked to peer-to-peer file sharing networks. This build, marked as version 1096, inadvertently acted as a fully-functional tech demo of S.T.A.L.K.E.R.’s engine, despite its lack of NPC enemies and fauna.
At the end of February 2009, due to popular demand GSC Game World released “xrCore” beta build 1935, dated October 18, 2004. It uses a completely different physics engine with many cut monsters, levels, and vehicles. It was also significantly larger than the retail release. It is however somewhat unstable, but features the full game along with a “fully functional ALife system”. It is currently available for free download from the GSC servers and mirrors. Also, oldest leaked builds of the game can be found in here.
Below you can see many videos from STALKER’s prototypes, alpha and betas. More videos and links can be found in the STALKER beta topic in our U64 Forum. Thanks to Megalol for the contribution!