The medieval grand strategy Crusader Kings II is free for a limited time on Steam. The game normally costs 39.99 euro but for the next 48 hours you can get it for free.
To get the game, just go to the Crusader Kings II page on Steam, and click the "Install game" button. Once you get the game, it will be yours forever. The offer ends on Saturday, April 7 at 10 a.m. PT.