CodeCity is written by Richard Wettel and is an integrated environment for software analysis, in which software systems are visualized as interactive, navigable 3D cities.
The classes are represented as buildings in the city, while the packages are depicted as the districts in which the buildings reside. The visible properties of the city artifacts depict a set of chosen software metrics, as in the polymetric views of CodeCrawler.
Here is an example of a city generated for the ArgoUML Java system:
For more details you can check the official website.