Slender - Catch all
So until recently I've been able to honestly say that no game has scared the hell out of me quite the way that Slender has. Slender is nothing more than you, your flashlight, some trees and a very lanky man that wants nothing more than to do horrible things to you. The only goal the game has for you is to collect 8 random pages that are spread around the fenced off forest that your in. The more pages you collect the more ambient sounds are added and the more terrifying things become.
You can download it here http://www.mediafire.com/?vql3a6fbjq... (I don't know if I can put links or not yet so it might not work)
its only 55MB and is only maybe 10 minutes long. But I highly recommend that anyone give this a try.
oh by the way. its also free.