OpenSCAD
A script-driven, programmer-oriented 3D CAD modeller that compiles a description file into a solid model, using constructive solid geometry and 2D-outline extrusion rather than interactive sculpting.
OpenSCAD creates solid 3D CAD objects from a script rather than through interactive modeling, focusing on CAD-style precision for parts such as machine components rather than the artistic modeling of tools like Blender.
It supports two main modeling techniques: constructive solid geometry, combining shapes with operations such as union, and extrusion of 2D outlines, using the DXF format to exchange those outlines and design parameters. It can also read and create 3D models in the STL and OFF formats.
It is free software available for Linux/UNIX, Windows and macOS.