FreeCAD - An open-source parametric 3D modeler
SketchUp - 3D for Everyone
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
SolveSpace - SOLVESPACE is a parametric 3D CAD program with extrude, revolve, union and difference functions.