Unturned is a survival sandbox game created by a guy named Nelson Sexton and is available on Steam. The zombie apocalypse has happened, and you are the sole survivor. You and maybe a few of your friends. And perhaps over 50,000 other people.
But don't lose hope! The zombies currently aren't all that dangerous. You can kill them with your bare hands if you want to. The real objective is simply to survive. Unturned is basically a little Don't Starve, a little Minecraft, and a little DayZ mixed together. You have to manage your nutrition and sickness levels by looting while looking at blocky graphics, dealing with an inane crafting system and occasionally driving a car.
The game does support multiplayer, but doesn't have an in-game server browser. Instead, you look up servers on the Steam discussions board for the game and then connect manually. Before jumping into multiplayer, though, you might want to do some reading. Check out tips and guides, because there is very little direction given, and the game can get pretty deep if you have the patience. Fancy guns and big houses can be yours if you can only figure out how to make them.
Unturned seems to be in good hands. The single developer updates very often and the future of the game looks brighter than the games it took inspiration from.