Underhell is a Source Engine game developed by the Underhell Team in collaboration with We Create Stuff.
Underhell Chapter 1 requires ONLY Source SDK Base 2007 installed.
No Source game is required.
Underhell Chapter 1 Trailer has arrived! It features a lot of voices from many different conversations throughout the game.
This should give you an idea of what to expect as far as ambient and immersion is concerned.
Mod DB Page : Desura.com
Website : Underhell.wecreatestuff.com
Steam Community Page : Steamcommunity.com