Ondsel is a general purpose feature-based, parametric 3D modeler for CAD, MCAD, CAx, CAE and PLM, aimed directly at mechanical engineering and product design but also fits a wider range of uses in engineering, such as architecture or other engineering specialties. It is 100% Open Source (LGPL2+ license) and extremely modular, allowing for very advanced extension and customization. Ondsel is based on FreeCAD, a free and open source project.