This is weapon pack, that contains almost ~200 weapons for different slots. Original mod ("Special Arsenal") belongs to @Josh771. It can be combined with monster or/and map packs to increase pleasure.
A versatile HUD mod - Recommended and essential for best experience with S.T.A.L.K.E.R. Weapons. This one also fixes a bug that was preventing it from loading with latest GZDoom (4.7.1).
What is the map you are using in the screenshot?
it's from a game called STRIFE