GoG Mount & Blade, a mixture of role-playing and strategy game, turns the players in a fantasy world into a mediaeval leader. Further parts of the series are offered in the same period with a discount of 75 percent.
To get the game for free, just click on the big action banner at the top of the GoG homepage. The title is automatically added to the game library, although not immediately. A free user account is required to participate in the promotion.