Wikipedia
OpenSCAD
OpenSCAD is a free software application for creating solid 3D CAD objects. It is a script only based modeller, with a specific description language. Parts cannot be selected or modified by mouse in the 3D view. An OpenSCAD script specifies geometric primitives and defines how they are modified and manipulated to render a 3D model. OpenSCAD is available for Windows, Linux and OS X. It does constructive solid geometry (CSG).
As of 2016, it uses Computational Geometry Algorithms Library (CGAL) as the basic CSG engine, which along with other libraries takes care of details such as intersection, difference, envelope combination and Minkowski sums.