Zombies and co-op are the ideal genre mashup. Whether you're surviving the endless rounds in Call of Duty Zombies, pushing through infected hordes in Left 4 Dead, or chopping off limbs in Dead Island, it's always better with friends. This is something that Ultimate Zombie Defenseperfectly understands, as it embraces the chaos and teamwork required to make it through unscathed. Now's the time to give it a try, too, because you can add it to your Steam library for free. Don't wait up, though, because this offer isn't sticking around for long. Continue reading Snag chaotic co-op game Ultimate Zombie Defense for free right now, but act fastMORE FROM PCGAMESN: Best zombie games, Best co-op games, Best survival games