Dark Pathogen Studios made a series of games similar to Slender. Same game play, same monster, different environments. The first game in The Slender Man's Shadow series is called Sanatorium. They have made several more since. Below is a link to where you can download the games and PewDiePie's playthrough of Sanatorium.
http://www.slendermansshadow.com/
http://www.slendermansshadow.com/