Most Computer Aided Design suites integrate mechanical simulation too. They can compute loads, stresses and so forth too. They even simulate gases and liquids

Most Computer Aided Design suites integrate mechanical simulation too. They can compute loads, stresses and so forth too. They even simulate gases and liquids etc, so they can 'run' combustion engines and so on virtually. There are some really neat videos on the Autodesk and Solidworks websites, and doubtless there are other CAD suites doing this too.