Urban is a software capable of procedurally creating 3d urban environments. It's based on a multi-agent system where each agent is responsible for one type of urban object. This means the system is highly modular and can easily be extended.
The Deimos Project is a Java-based game development library collection. Includes Vertex Modeler, a 3D modeler that lets you programatically define models using Java source code. The modeler is also a simple scene graph API.