Emulators are software which allow one system to simulate the functions of another.  Many people have written freeware emulators which allow your PC to emulate many different video game consoles.  While emulators aren't perfect and can never replace the real thing, they can often perform most of the functions of the system they're emulating.  Here you can download emulators for systems represented in The Vault.  While there are dozens of emulators available, these are the best!