Slender: The Eight Pages, formerly known as Slender is a free experimental game developed by Parsec Productions. It was released as a beta in June 2012 for Windows and Mac OS X.
This game has a simple, yet effective formula, meant to scare even the bravest man in the world. This game is great (nor excellent neither epic. Just great. And not even close to "Best Scary Game Evah!"), but it's so overrated and already boring to play it doesn't make sense to play this anymore. After you get the last page, you lose your motivation to play Slender again.
Yes, the graphics are a little bad, but who cares anyways. Still, it made me jump many times and the atmosphere absorbs the player instantly.
For an experiment, it worked quite well.