BRL-CAD - Military Developed CAD

BRL-CAD is "a powerful Constructive Solid Geometry (CSG) solid modeling system with over 20 years development and production use by the U.S. military. BRL-CAD includes an interactive geometry editor, parallel ray-tracing support for rendering and geometric analysis, path-tracing for realistic image synthesis, network distributed framebuffer support, image-processing and signal-processing tools." What they said.