RCOM or 'Realistic' 'Combat' 'Overhaul' 'Mod' is a mod for S.T.A.L.K.E.R. - Call of Pripyat that aims to bring in a greater emphasis on realism. Additionally porting 'Clear sky' Levels to 'Call of Pripyat' which have been filled with new A-Life and content.
A video with some new features. Instead of listing them, I'll just let you watch and see what you can notice. The teaser's focus on the new feature is pretty obvious though.
Note: Forgive the ugly debug text that occasionally shows on the HUD. :)