Wow, I have not heard of this game until today, Its called Nation Red and heres a quick description,

“is an arena-based shooter providing a close-quarter battlefield experience. Fight thousands of zombie mutants and their bosses in frantic bloody game play. Play the demo for free.

Features Exclusive to purchasers on Steam:

• Steam Hammer — Rips the skin off your opponent (nice)
• New Level and New Enemies — Zombie patients and caretakers in a desert asylum
• Pneumatic Destroyer — Detonates the Thumper (a road construction compactors) once it is surrounded by zombies”

This game is only $7.50 on Steam right now, http://store.steampowered.com/app/39800/

I’m definitely getting this game it sounds like a lot of fun. Check out the trailer here