UnBBoolean is a fabulous 3D modeling tool that employs Constructive Solid Geometry (CSG) operations on primitives (i.e. boxes, cones, cylinders and spheres). It was developed by Danilo Balby (email@example.com).
Using just three CSG operations (union, intersection, and difference), its possible to create very pleasingly complex shapes in just a few steps. UnBBoolean allows these shapes to be saved in its CSG format so they can be edited later, or exported as an OBJ mesh. UnBBoolean proved very popular, and has been ported to various other languages and libraries.
Balby moved on to other things, and development of the project halted in 2009 (at http://unbboolean.sourceforge.net/). Unfortunately, that means that UnBBoolean won't compile with the latest version of Java 3D (and it has a few problems with the latest versions of Java too).
I spent a 1-2 hours updating the code, making a few other very minor modifications. This version of UnBBoolean (v 1.2) can be downloaded as a zip file (13.6 MB). The size reflects that it includes the JAR files for Java 3D and JOGL, so only needs Java. There's a README file on how to run the tool, and a few examples.