try day of the zombie it is awesome i have played it for a while but the only problem i have is that it does not have a really good survival like collect the food so you don't go hungry get bars of granola for stamina and find pills to keep your health up kind of game here is the download
if you are looking for the collect the food so you don't go hungry get bars of granola for stamina and find pills to keep your health up kind of game try state of decay on xbox 360 it costs though so day of the zombie is about the best you are going to get for free
Sorry dude I am looking for the same thing and the closest thing I got was to download Arma 2:free go to multiplayer and find a server with the mission of "Dynamic Zombie Sandbox" that is supposed to be like Dayz but it isn't very good because (A.) the only way to find loot is to find weapon crates or find weapons in vehicles and (B.)IT DOESN'T SAVE YOUR PROGRESS so if you find the best loot it is worthless when you log off. So you can go download Arma 2 :free and here is the link if you want to do this : http://www.arma2.com/supply/free.html
No More Room In Hell and Unturned. The second one is on green light and is a WIP (work in progress just in case u don't no.) NMRIH is a great game but you need a small group to do anything. The maps are small but with friends are fun. It has server, single player and LAN capabilities. On Unturned I haven't successfully played multiplayer yet but I hear that it has Minecraft like server hosting. It has a pretty large map and lots of things to do so check it out if ur willing to.