FreeCAD

FreeCAD is open-source parametric CAD with no price tag, no revenue cap, and no account requirement — download it and it is yours to keep using. Recent versions have closed much of the gap with commercial tools on sketching, assemblies and rendering, and because it is open source, its file formats and internals are fully documented rather than locked to one vendor.

The trade-off is polish and consistency: workflows that feel obvious in SolidWorks or Fusion sometimes take an extra step or a workbench switch in FreeCAD, and community-written documentation is not always as current as the software itself. None of that changes what it produces — a fully dimensioned, feature-driven solid model — which is exactly what every exercise on this archive asks for.

Choose FreeCAD if budget is the deciding factor, or if you specifically want to learn on open-source tools.

Against Fusion's free Personal Use plan and Onshape's free tier, FreeCAD is the only one of the three with no revenue cap, no document limit and no requirement to work in the cloud — the trade-off is a rougher, less consistent workflow than either. Against Alibre Design, the other budget-focused option here, FreeCAD costs nothing at all but is less polished out of the box.