Any good VMS – Virtual Machine System ?

I have been day dreaming an OS that can switch from Dos to Windows XP to Mac to Linux with a few key strokes. Sitting only on a typical hardware in the store. It can get booted within a second running ‘bare’ mode to service services. It can run any kind of desktop application too.

Is there such a thing out there ? If not, do you think its worth while to build one ? Would you get a copy if it is free, $10, $100 or $1000 ?