So this game "Guns up!" on steam hit me by surprise...
There are a few "modes" in which you play:
1.) [Attack] - Attack other players bases by sending units and using strategic items to victory.
2.) [Defend] - Other players attack your base and you have to make sure your base is ready for random attacks by placing strategic choke points.
While all this is going on, you earn random currencies, cards, units etc... by playing the game... Its actually very addicting and very challenging....
100% Free and the cash shop is very optional, you can earn everything in game. http://store.steampowered.com/app/446150
So glad I found this game!