Algodoo - gives you the opportunity to play with physics. Use your own hands and simple drawing tools to design, construct and explore the world of physics.
Algoryx Momentum - If Algodoo not technical enough for you, check this out.
Algoryx Momentum is about Motion Dynamics and modern engineering. About developing, verifying and visualising the function and performance of mechanical systems. And ultimately achieving reliable, efficient and hugely successful engineering solutions.