The real-time strategy Sins of a Solar Empire: Rebellion is free for a limited time through the Humble Store. The game normally costs 39.99 euro but for the next 72 hours you can get it for free.
To get the game, just go to the Sins of a Solar Empire: Rebellion page on the Humble Store, and click "Get the Game" Once you get the game, it will be yours forever. The offer ends on Sunday, November 18 at 10 a.m. PT. But be careful, because the keys cannot be redeemed after November 22.