Clive Barker's Undying is described as 'The game begins in 1923, after World War I veteran Patrick Galloway receives an urgent letter from his friend Jeremiah Covenant'. There are more than 25 games similar to Clive Barker's Undying for a variety of platforms, including Windows, Mac, Steam, Linux and Xbox. The best alternative is Half-Life. It's not free, so if you're looking for a free alternative, you could try Hexen II or SCP: Containment Breach. Other Clive Barker's Undying like games are Left 4 Dead (Paid), BioShock (Paid), Borderlands (Paid) and Amnesia: The Dark Descent (Paid).
Slender: The Eight Pages is a free indie-developed psychological horror/survival horror video game for Microsoft Windows and OS X. The game is based on the Something Awful forums' creation, Slender Man.
SCP: Containment Breach is an indie survival horror video game based on the stories of the SCP Foundation website. The player guides a test subject, D-9341, through many obstacles inside of a facility belonging to the shadowy SCP Foundation.
After a secretive agency in New York is invaded by an otherworldly threat, you become the new Director struggling to regain Control in this supernatural 3rd person action-adventure from Remedy Entertainment.
Bulletstorm focuses on combat, both with firearms and melee attacks. There are a variety of fictional firearms available, although the game also places heavy emphasis on kicking enemies and using the energy leash.