SolveSpace

SOLVESPACE is a free (GPLv3) parametric 3d CAD tool.

Applications include:
Modeling 3d parts — draw with extrudes, revolves, and Boolean (union/difference) operations
Modeling 2d parts — draw the part as a single section, and export DXF, PDF, SVG; use 3d assembly to verify fit
3d-printed parts — export the STL or other triangle mesh expected by most 3d printers
Preparing CAM data — export 2d vector art for a waterjet machine or laser cutter; or generate STEP or STL, for import into third-party CAM software for machining
Mechanism design — use the constraint solver to simulate planar or spatial linkages, with a pin, ball, or slide joints
Plane and solid geometry — replace hand-solved trigonometry and spreadsheets with a live dimensioned drawing