If you really want to emulate on Mac but, say, can only get at your machine via SSH, have I found some options for you!
https://github.com/hasegawa-tomoki/php-terminal-nes-emulator
(only works for Mapper 0, and is limited at that, laggy as heck but still impressive)
https://github.com/gabrielrcouto/php-terminal-gameboy-emulator
(actually seems frighteningly decent all things considered)
Edit: ok, Link's Awakening works frighteningly decently until you get control and realize you can't really hold buttons. Shantae just blows everything to heck. Final Fantasy Legend II... is being uncooperative...?