If you’ve looking for open source 3D modeling software that focuses more on the CAD and less on the artistic/game dev aspects, consider Openscad. Think design of machine parts, not movie animation. It takes a different approach than other 3D modeling software.
OpenSCAD is not an interactive modeler. Instead it is something like a 3D-compiler that reads in a script file that describes the object and renders the 3D model from this script file (as in the example above). This gives you (the designer) full control over the modeling process and enables you to easily change any step in the modeling process or make designs that are defined by configurable parameters.
Visit the Openscad website to download the software today.