Not technically a Mac-exclusive emulator but still pretty cool. Gave it a bit of a go yesterday and was playing for ages!

Gameboy Online



EDIT: More info and source code here.

not going to evaluate it now, but it looks cool. Reminds me vaguely of an online NES emulator I saw ages ago which also gave a real-time view of the loaded tilesets and palettes...

I suppose theoretically this should work on iOS devices, although as you have to use the keyboard to control games I can't really try! Compatibility has been great for me so far though, anyone else given it much of a go?

This website has not only GameBoy games but also, SNES, NES, Master System, Commodore64 and even DOS games playable in your browser via Java: Nintendo8