polygon.city is a project aimed at collecting, converting, and distributing open-source 3D building data. Its current focus is the conversion of CityGML files into more easily-parseable flat object files using https://github.com/polygon-city/polygon-city-cli.
Right now we're looking at these cities in particular: polygon-city/polygon-city-cli#22
And here are a couple of works in progress:
- Linz, Germany: https://github.com/polygon-city/polygon-city-linz-export
- Berlin, Germany: https://github.com/polygon-city/polygon-city-berlin-export