The Stanley Parable is a first person exploration game. You will play as Stanley, and you will not play as Stanley. You will follow a story, you will not follow a story. You will have a choice, you will have no choice. The game will end, the game will never end.

User reviews:
Overwhelmingly Positive (1,188)
Very Positive (27,702)

Release Date: 17 Oct, 2013

The key is from a pretty old Humble Jumbo Bundle 4 which I forgot about.

Enjoy!