Please note that this is an old demo that has since grown into a full-blown game: https://steamcommunity.com/app/1291340 (Says Windows-only, but has a working Beta for Mac)
That looks like a great creative app. I wonder how much work it would be to build realistic-looking replicas of modern cities using this - I guess it would need almost as many styles as there are buildings.
Here's a talk by Oskar on how generating such worlds work: https://www.youtube.com/watch?v=0bcZb-SsnrA