When STALKER emerged from development hell in 2007, the final product met with an unexpectedly positive reception. For those more interested in a slice of that development hell, though, developers GSC have you covered.
An early, playable build of the game - dated October 18, 2004 - has been released by the team, giving you all a glimpse at some of the game's unused areas. You can grab it at the link below.
We can't remember the last time a developer did this (if indeed it's ever been done), but would love to see more of it. It's like a gaming equivalent of the director's cut.