Open Source CAD Software
A CAD model is rarely a one-off - it's an asset you revisit for years as a part gets revised, a building gets renovated, or a design gets reused, so a proprietary file you can only open while a license is current is a liability disguised as a deliverable. The open source tools here build parametric, 2D, and code-driven designs in open or scriptable formats, so the geometry you defined stays editable on your own terms instead of being held by whatever wrote it.
FreeCAD
Parametric 3D modeler for product design, mechanical engineering, and architecture
OpenSCAD
Script-based solid 3D CAD for precise models, with CSG and 2D outline extrusion
LibreCAD
Cross-platform 2D CAD program for technical drawing with DXF and DWG support
CadQuery
Python parametric CAD scripting framework for building customizable 3D models and exporting STEP, DXF, STL, and more
SolveSpace
Parametric 2D and 3D CAD with a constraint solver for sketches, parts, and assemblies
KiCad
Electronics design suite for schematic capture, PCB layout, and 3D board viewing
build123d
Python CAD-as-code library for parametric 2D and 3D BREP modeling on the Open Cascade kernel
QCAD
Cross-platform 2D CAD for technical drawing with DXF support and a scripting interface
BRL-CAD
Combinatorial solid modeling system with a 3D geometry editor, ray tracer, and analysis tools