A spare from the recently expired Double Fine Humble Bundle. To the best of my knowledge there is no region-locking at play, but by taking part in the giveaway you accept the off chance of not being able to validate the key by reason of region-locking, and you commit yourself to accepting a no-fault cancellation of the giveaway, and to not keeping the serial key unused so that a new region-locked giveaway can be run.

Are you interested in game documentaries?