Generation Exile, a city builder which just released on Steam in early access, has a killer plot: Earth is dead or dying, ruined first by ecological collapse and finished off by the gruesome genetically engineered things we thought would fix it. A colony ship is set to undertake the multi-hundred-years journey to a new world orbiting a new star, and the ship's huge compartments hold microcosms of Earth's biomes to feed the crew and repopulate the new world.
The only problem is that the engineered life forms, the Scale, have somehow made it on to the ship and now everything has gone very, very wrong. You and your people have hidden in the maintenance tunnels, but now the monstrosity is colonizing them too, so you've got to go into the biomes and build yourselves sustainable communities from the wreckage there—a landscape now populated by weird mutants that the Scale left in its wake.
