I have been playing Unturned for 4-5 days now. It is like Minecraft & DayZ slammed together. You are thrown in forced to survive against zombies. Scavenge for supplies to survive, Build a fortress, and create traps to defend while you are away. It is free to play and isn't that bad for having only one developer that brings updates quickly. Multiplayer requires Tuungle, Hamachi, Evolve, etc. Keep in mind it is in Early Access, so this isn't the final game but worth checking out.
Video of our trailer to the Unturned Series made by my good buddy Feisty Gorn.