Ben Firshman wrote a rather impressive NES emulator. There are already quite a few NES emulators out there already this one impressive is because it’s written in pure JavaScript.
Yet another application of “Atwood’s Law“:
Any application that can be written in JavaScript, will eventually be written in JavaScript.
I should note that I mentioned back in January how someone ported Super Mario brothers to JavaScript. JSNES is different as it is actually emulating and reading ROM’s (looks like they are hex’d), rather than just replicating the game.
Currently it runs in all modern browsers, but only Chrome’s <canvas/> performs well enough at this point to really be playable. With WebGL coming to Firefox and WebKit we’ll hopefully see a lot more of this kind of stuff in the future.