FreeCAD

FreeCAD is a powerful, open-source parametric 3D CAD modeler aimed primarily at mechanical engineering and product design but extensible to architecture. Its modular architecture allows workbenches for specific tasks like Sketcher, Part Design, and FEM simulation. Being completely free and open-source, it offers incredible value for hobbyists, students, and professionals on a tight budget. While its interface and stability may lag behind commercial giants, its active community, Python scripting, and zero cost make it a highly-ranked, viable option for learning parametric concepts and completing serious design work without financial investment.