" Grab em by the PU55Y. "

FREE STANDALONE STALKER MOD: ANOMALY

https://www.moddb.com/mods/stalker-anomaly

"Anomaly is a standalone S.T.A.L.K.E.R. mod powered by an x64 version of the X-ray engine.."

Also check SPC: Unity for free
https://www.scp-unity.com/

SCP: Unity
A single-player exploration game with survival horror elements built in Unity by an expert team of passionate developers and artists.
Experience the SCP universe brought to life as you explore and try to escape the containment breach of ARC-Site 48.