CityDoctor2
CityDoctor2 is the name of a research project (see here) and a software which aims to validate and automatically repair CityGML files. The GUI can be downloaded here.
It can validate CityGML files and report on any missing requirement necessary for simulation. Some simulations have more requirements than others and CityDoctor2 can be configured with a validation plan that only checks the necessary requirements. It is a prerequisite for simulations to have a valid dataset to work on.
Additionally, an automatic healing part is in development which will be able to repair some of the more common problems e.g. wrongly orientated polygons.