www.playrust.com$20 right now via paypal, and then a code is sent to your email which can be used to activate the game on Steam. It is currently in Alpha and has tons of potential -- already it has made just under a million in sales.
Like DayZ it is a world with survivors and zombies. The game is standalone and not a mod, so it was designed for how it is played, making it not nearly as clunky and slow as DayZ. It features much more natural survival elements unlike DayZ's urban survival focus.
It is a great game, worth every dollar I paid, and it is only going to get better. If I had to describe the game I'd say it is a combination of DayZ, Minecraft, and Terraria. The devs are actively listening to the community on the Rust forums. If you're a DayZ lover you'll love this game too.