Blender is a open source 3D content creation program.  While it's usually not at all well-suited for engineering, scientific, and other CAD purposes, it's a popular content editor that is really good at some forms of editing (surface editing in particular).

This task has you write a tutorial on how to model something in Blender, export it to a file, import that file into BRL-CAD, and render the imported geometry.  Include lots of screenshots for every step along the way.

Note that to import geometry into a CAD system like BRL-CAD, you're going to need to model something that forms a closed volume.

References:

• http://www.cs.auckland.ac.nz/~jing/opengl/blender3dtutorial.htm
• http://www.blender.org/education-help/tutorials/

Tools:

• blender
• *-g (we have lots of importers, e.g., step-g, dxf-g, stl-g)
• mged (display and edit geometry, run "tops" and "draw" commands)
• within mged: rt -s1024 -A0.75 -c {set ambSamples=128} -c {set ambSlow=1}