VMWare is a commercial VirtualMachine that emulates an entire PC in a PC.

VMWare is special in that it makes an unusual assumption to allow for an unusual optimization that allows for unusual performance of emulated code: VMWare requires a PC to run. Instead of emulating the CPU, that is, interpreting every single MachineCode instruction in the code running under emulation, it instead only intercepts the execution of instructions needed to set up its smoke and mirrors. "Normal" instructions runs non-emulated on the real hardware CPU. The result is blazing fast emulation, unrivalled by any competitor.