The SGM mods come from the Russian Mod Community, They extend the vanilla storyline with additional quests, From version 2.0 on they also add extra maps found in the Clear sky game. As well as quests and maps you also get many new items, weapons, outfits and artifacts. The versions here have had additional mods merged with them such as Atmosfear and Absolute Nature as well as any fixes, tweaks and translations required.
SGM 1.7, Vanilla.
SGM 2.0, Vanilla & Dark valley.
SGM 2.1, Vanilla, Dark valley, X-18, Military Warehouses, Agroprom & Agroprom underground.
SGM 2.2, Vanilla, Dark valley, X-18, Military Warehouses, Agroprom, Agroprom underground, Red forest, Cordon & the Marshes.
In SGM you can also join factions and take on faction specific tasks.
The factions you can join are:
Dawn (Remnants of Clear sky),
& the Monolith.
Video of original development team:
Вольные Сталкеры. Скрины из SGM-mod.Мы ЕСТЬ! - YouTube