past few weeks I've been wanting a Open World Survival Zombie game and I was looking online and I saw Rust, watched some videos and the game looks pretty cool and exactly like what I wanted, zombies, building, survival. :3
You should be aware that:
a) This game is a very rough alpha (meaning: buggy, server may go down at random, the game might just break) and everything is subject to change
b) Zombies are a temporary placeholder enemy and will be removed completely later on in development when real monsters are available (unless that changes and it keeps the zombies, who knows)