OpenSCAD - OpenSCAD is a software for creating solid 3D CAD objects.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
FreeCAD - An open-source parametric 3D modeler
SketchUp - 3D for Everyone
OpenJSCAD.org - OpenSCAD + JavaScript = OpenJSCAD, edit locally or remote online, preview in browser direct via...
CadQuery - CadQuery is a parametric cad script framework