OpenSCAD is an open source programmatic CAD program. If you're a programmer OpenSCAD will be very familiar.
Blender is a free and open-source 3-D computer graphics software product used for creating animated films, visual effects, art, 3-D printed models, interactive 3-D applications a...
BRL-CAD is a cross-platform solid modeling system. It's been continuously developed for over 20 years, and is still in active development; it's participated in Google Sum...
FreeCAD is a parametric 3D modeler. Parametric modeling allows you to easily modify your design by going back into your model history and changing its parameters. FreeCAD is open...
QCAD is a free computer-aided design (CAD) software application for 2D design and drafting. It is available for Linux, Apple OS X, Unix and Microsoft Windows. The QCAD GUI is bas...
LibreCAD is a free, cross-platform 2D CAD application. It works on Windows, Mac OSX, and Linux, and is available in over 20 different languages. The source is available on github.