OpenSCAD
Release status: WIP
OpenSCAD is a free software application for creating solid 3D CAD objects. It is not an interactive modeler, but rather a 3D-compiler. OpenSCAD reads from a script and renders a 3D model from it. OpenSCAD is available for Microsoft Windows], Linux and Mac OS X. It does constructive solid geometry (CSG). OpenSCAD can also extrude forms from AutoCAD DXF files.
As of 2011, it uses Computational Geometry Algorithms Library (CGAL) as the basic Computational Solid Geometry engine, taking care of details such as intersection, difference and minkowski sums. The results can be rendered into 3D STL (file format)|STL files. It uses OpenCSG and OpenGL for fast previewing of models: rendering with CGAL (as with other CSG geometry engines) can sometimes take several minutes or hours.
-- Wikipedia