http://www.proceduralcity.com/
I’d say this is even better than all the previous engines designed to build cities because not only does it allow huge cities, it also allows.
-Every building to have an interior
-Every building to have their interiors destructable so you can shoot up the inside of each floor.
It would’ve been a lot cooler if you could blow holes in the roof, floor, and outer walls as to make the whole building collapse into a heap of rubble, but it’s pretty impressive work for what has been done so far.