The team-based (not turn-based) tactical shooter Insurgency: Sandstorm will be out on September 18, and to convince everyone to give it a try, New World Interactive is giving the original Insurgency away for the next two days.
Insurgency is a multiplayer tactical shooter that encourages teamwork through a "brutal" commitment to realism, which in the context of videogames means no regenerating health and certain death if you take more than one hit. It's good—we scored it 77/100 in our 2014 review—and the player base has remained active enough (in the low to mid-2000s) to keep it viable over the four-plus years that it's been out.
To get your free game, just pop over to the Insurgency Steam page before 10 am PT/1 pm ET on August 15 and click the "play game" button. It'll be added to your library, and you'll be prompted to begin the install process. Having the game in your Steam library will also net you ten percent off the price of Insurgency: Sandstorm, which comes in on top of the ten percent pre-purchase discount.