The S.T.A.L.K.E.R. community has created massive "standalone" mods that use the game's engine and assets but do not require you to own the original game files to run. These are widely considered the "best way to play for free" legally due to the developer's historically relaxed stance on modding.

S.T.A.L.K.E.R.: Call of Pripyat system requirements - Can You RUN It

: An even more advanced modular expansion built on top of Anomaly . While it technically suggests owning the original games to support the devs, it is distributed as a free, independent installer.

: Provides a DRM-free version, meaning no internet connection or activation is required once downloaded.