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.
One of the best Call of Pripyat mods out there, even if the most challenging. Despite a very vanilla appearance, many aspects of the game have been nicely overhauled, resulting in very realistic, life-like weapons, self-aware and more cautious combat AI, medical kits that don't make you immortal for 10 seconds, and very plausible outfit protection characteristics. If you want to turn S.T.A.L.K.E.R. into the most entertaining indie FPS around, RCOM is what you want.