The complete source code of Stalker: Clear Sky and Stalker: Call of Pripyat were leaked last year. Based on that source code I am currently writing an OpenGL backend for Clear Sky: github.com/Armada651/xray/
This video shows the progress made compared to the previous video: https://vimeo.com/144270704. This time we’re showing a fully functional OpenGL backend with no visible graphical glitches. My effort is now focused on bringing this backend to Call of Pripyet (XRay 1.6) and implementing DX10-level features. Meanwhile the team is working on porting the engine code to Linux.
If you’d like to contribute leave a comment and be sure to join the IRC channel #openxray @ irc.freenode.net.