FreeCAD

freeCAD is a basic 3D CAD with advanced Motion Simulation capabilities. It is suitable for anyone interested in learning 3D CAD and Motion Simulation for free before using more sophisticated packages. Its motion simulation capabilities are comparable to the best and can provide accurate answers to engineers and scientists in diverse fields. Educators, students and new engineers will find it ideal for the teaching and learning of geometry, kinematics, dynamics, vibrations, mechanisms, linkages, cams, machine design and physics. The program runs on Windows, Linux PC, Macintosh PPC and other Unix's. Assembly data are unchanged across platforms.