Structure Synth generates 3D structures by specifying a design grammar. Even simple systems may generate surprising and complex structures. Structure Synth offers a graphical environment with multiple tabs, syntax highlighting, and OpenGL preview.
A version of the source I used in these videos on youtube: http://www.youtube.com/watch?v=5k6arok7zac http://www.youtube.com/watch?v=TaNu8-ObsXU and http://www.youtube.com/watch?v=7qAq61ATgqo . It requires Sunflow, JBullet, and Java.
Sunflow is a rendering system for photo-realistic image synthesis. It is written in Java and built around a flexible ray tracing core and an extensible object-oriented design.