Steam is offering Geneshift for free. The game has been under development for 9 years and is not quite complete. Meh. Its free until December 19th 10AM PST to sign up (permanently free to play)
Geneshift is a GTA-inspired battle royale where each round lasts only two minutes. Use exploding cars, miniguns, invisibility, and more to outplay friends in tactical online combat. Loot for special powers, build secret bases, and be the last man standing!
Runs on Windows and Linux.
Very Positive reviews on Steam