FreeCAD
FreeParametric 3D modeling — change one dimension and the whole model follows
Open-source parametric 3D modeling. Models are built from dimensioned sketches and features, so changing any parameter recomputes the whole part. It covers part design, assemblies, technical drawings, finite element analysis and CAM, and exports STL for 3D printing. Free for commercial use. The Windows installer is about 495 MB.
Why we picked it
Parametric modeling is a different activity from "drawing a 3D shape". You start with a dimensioned sketch, extrude it into a solid, and later — when a hole needs to go from 5 mm to 6 mm — you change that one number and every dependent feature recomputes. No redrawing. This is how SolidWorks and Fusion 360 work, and FreeCAD offers the same paradigm.
32,850 stars, LGPL-2.1. It is organized into workbenches: part design, sketcher, assembly, technical drawing, finite element analysis, CAM, architecture/BIM and ship design each swap the interface and tools to that domain. Which means it is not "a 3D printing app" or "a mechanical app" — it is a platform.
For 3D printing it is genuinely practical: model the part, export STL or 3MF, drop it into your slicer. Compared with sculpting shapes in a mesh tool, parametric modeling is overwhelmingly better for functional parts — clips, brackets, gears, enclosures — in both precision and revisability.
Two things to be ready for:
- The learning curve is steep. Parametric CAD requires building an intuition for constraints, and FreeCAD's interface is unapologetically engineer-flavoured, so the first few hours are frustrating. Follow one complete beginner course rather than clicking around.
- The download is large (about 495 MB on Windows, around 783 MB for the Linux AppImage), because a Python runtime and a pile of solvers are bundled in.
The 1.x releases improved stability and the long-standing topological naming problem considerably over the old 0.x line. If you tried it years ago and gave up, it deserves another look.