So, This mod has been released for a few months now and the current version 1.3.09 is very stable.
So in short, a sandbox freeplay version of the stalker series. It covers all the maps from all three games from the Cordon and swamps, right through to the NPP and also includes the three CoP maps as well, and an original map just for CoC.
The ability to join any faction such as the loners, clear sky, the bandits and even the military as well as a few others.
Another amazing feature is the amount of addons developed so far for the mod, from new models for npcs, arsenal and weapons mods, to a new game mode called factions wars where you take direct control of a faction (not one I have tried yet myself) and dominate the maps.
I've put quite a few hours into it already and foresee many more as more and more addons by other modders are made.
Not only was CoC made to be a decent stalker free play experience, it is a significant modder's resource.
Requires Stalker Call of Pripyat to be installed however CoC is essentially a stand alone game installed in a separate folder with it's own launch executable.
(Sorry if the writing is not up to par, it's too damn hot and writing is not my forte)