OpenSCAD

OpenSCAD is a software for creating solid 3D CAD objects

OpenSCAD is a software for creating solid 3D CAD objects. It is free software and available for Linux/UNIX, MS Windows and Mac OS X.

Unlike most free software for creating 3D models (such as the famous application Blender) it does not focus on the artistic aspects of 3D modeling but instead on the CAD aspects. Thus it might be the application you are looking for when you are planning to create 3D models of machine parts but pretty sure is not what you are looking for when you are more interested in creating computer-animated movies.

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 (see examples below). 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.

OpenSCAD Web Site