Sort of surprised nobody has mentioned it but there is FPSE...
I think you didn't understand what i mean by "please be realistic" or perhaps you are just kidding?
interesting question but I think you have to narrow it down some, because of the different ways of emulation;
I'm interested in any decent game machine that a classic Amiga is able to emulate at a reasonable speed.
This means no Atari2600 (too primitive) and no Playstation (too slow) emulators.