S.T.A.L.K.E.R: Anomaly

The stand-alone mod S.T.A.L.K.E.R. Anomaly 1.5.1 aims to be the most stable and customizable experience for fans of the S.T.A.L.K.E.R. games. It's powered by the Monolith 64-bit engine, a custom fork of the X-Ray engine.

Players can choose from a variety of ways to play the mod. Play story mode with 4 chapters of interesting quests, sandbox mode if you prefer to make up your own story, or the combat intense warfare mode where factions fight for influence and control over different areas of the zone.

Anomaly is also highly customizable, play it the way you like and have the most fun. There are hundreds of settings that can be tweaked in the options menus and for more advanced changes, there are over 1000 addons for Anomaly that were created by other players to change the experience in more advanced ways.

More info on: https://www.moddb.com/mods/stalker-anomaly