Aren't you sick of all them "buy our game and now buy our partner's graphic card"-type horror games (and all other games, for that matter)?
Well, i got sick and tired of pirating famous commercial horror vg titles, just to be disappointed of them in the end. So, to avoid the bother, I decided to download a free, open-source, horror survival videogame.
The closest answer to my needs was
SCP Containment Breach
The only disappointment with it, is perhaps lack of further development, which is where you can come in and make a difference (open source, baby).
So, what's it about? Nothing special. You just walk around randomly-generated rooms, running away from... whatever scp you might encounter.
They even have a wiki that explains every scp and how to tackle them; sort of like a bestiary of creepypasta-like objects or life forms.
I could go on about the game, but you can see for yourself on youtube. One of the things i like about it is it's filesystem: allows for access, modifications, or even export of some media you might like. Even has a map editor, but even playing on a custom map won't make it less difficult.