The multiplayer Xbox Live Indie game, Take Arms, offers a ‘free’ port to Windows titled Take Arms: Bot War.
While being free, the game also offers a ‘pay what you want’ system when you head to the checkout. You can select a pre-determined price ranging from $1.00-$25.00 or pick the option to set your own price, which can be absolutely nothing.
The game features three different classes, game modes, and maps. Since it also doesn’t support online multiplayer, you’ll be fighting against AI bots instead. You can find the download and more information here.