SketchMonkey is a Java sketch-based modeling tool built on top of jMonkeyEngine 3.0 (http://www.jmonkeyengine.com)
This software was developed by Marcos Ramos (msramos at ic dot uff dot br) as part of requisites to achieve his Master's Degree in Computer Science.
Details of the techniques used and implementation can be found in the thesis (in portuguese). The thesis can be found in http://www.ic.uff.br (also in portuguese).
This software is provided "as is". No warranties. ;)