Created with 3fier, available in OBJ and CityGML.
Created with Random3Dcity, available in OBJ and CityGML.
Note that on our website CityGML.guru we also maintain a list of open 3D city models of cities around the world.
Furthermore, Wikipedia has a list of national lidar datasets. These datasets can be used as input to generate 3D city models. A possibility is to use the open-source software 3dfier developed at our group, or other CityGML software.