Frozen Synapse is Steam's Weekend Deal. This game is amazing, and has quickly become my go-to Multiplayer game and one of my favorite games of ALL TIME. It's a very strongly multiplayer-focused simultaneous turn-based strategy game, in which both players have a "planning phase" to plot out what their hand of 3-5 units will do, and the action plays out in an "outcome" phase, where both sets of units execute their plan and live or die based on a variety of factors(unit type, cover, movement speed, stance, and range). The fun is in trying to guess what your opponent will do, and what your opponent THINKS you will do, and planning for a variety of contingencies. The game has one feature that I think makes it: The ability to make test orders for your enemy's units and see what would happen if they did something. THIS really makes the game entirely about planning your next strike and less about knowing the complex numbers behind the scenes, because you can go "Well if he shot a rocket there, what would happen? If he moves his shotgunner here and then aims there, would my guy's ass be blown so far up his head the moon turns red?" Etc. It's tons of fun.
I strongly urge ANYONE with even the slightest leanings toward this sort of game to take the opportunity to pick this up, because it's simply an amazing and nigh-perfect game. When you buy it, you get two copies(one for yoruself, and a Steam gift), so you can even probably split this with someone to get it even cheaper.
Also, THERE IS A DEMO. YOU HAVE NO EXCUSE.