https://store.steampowered.com/app/304930/Unturned
Think of Day-Z in Roblox.
Built with Roblox, and on the steam platform, this is an open world zombie survival game and it is ruthless. You will die often. But you can craft, drive vehicles, etc…
Zombies are plentiful and resources scarce.
It updates a bit too often for my taste and there is a slight learning curve.
It is free and deadly.