The Steam version is being published by Midnight City, the indie label created by Majesco Entertainment earlier this year. Slender: The Arrival co-developers Blue Isle Studios and Parsec Productions originally released the game independently this past March on PC and Mac, but no Mac version is listed on the game's Steam page. Slender: The Arrival does support the Oculus Rift.
Midnight City also confirmed today that it is planning to bring Slender: The Arrival to unspecified consoles in the first quarter of 2014.
Slender: The Arrival stars a real estate agent named Laura who's helping her friend Kate sell some property. But Kate is missing when Laura arrives on the grounds, so she sets out with nothing but a camcorder and a flashlight to find out what happened. It is the only officially licensed Slender Man video game.