Unturned is a free-to-play steam game that was featured by Alpha Beta Gamer a while back. Unturned is a zombie survival game in a semi-blocky style in that the world looks normal, while entities, items, and vehicles are made out of blocks. This game features multiplayer with a server hosting style similar to Minecraft. This game is a serious challenge, but also a ton of fun to play. The map is predetermined, but everything else is randomly generated. The game has driveable vehicles and also is populated with animals that can be killed and looted, along with, obviously, zombies that will try to kill you. This game is open world and has no real goal, meaning you can do whatever you want. This is possibly the best free survival game on steam, and you can get it here.