A few days ago, the creator launched a Kickstarter for a stand-alone expansion: Mutant: Genlab Alpha. The premise sounds really cool:
In a remote mountain valley, mutant animals dwell under the watchful eyes of the mysterious Watchers. Kept prisoners for generations by electric wire and drones in the sky, never knowing who’s next to be dragged off to deadly experiments in dark laboratories, the animal mutants have had enough. The time for resistance is now. The fight for freedom has come.
The game has new powers, skills, rules, roles, and mutations for animal mutants, but is also compatible with Year Zero. That being said, it is a stand-alone game and you don't to have Mutant: Year Zero. Instead of focusing on building up the ark, the characters can strategically improve their tribes. Characters will also explore zones, just like the original. The book even includes a campaign focused on escaping the valley.
There's something about the game that just excites me. It reminds of Teenage Mutant Ninja Turtles and other Strangeness: After the Bomb, except I think I'll actually like this system. Check out the cover: