Baton.js
Use hardware MIDI devices in the browser
baton.js is a javascript library for working with hardware MIDI devices in the browser, using the new-ish WebMidiAPI.
The possibilities are endless!
Use a hardware MIDI controller or software MIDI sources like Ableton Live or Max/MSP!
Send MIDI notes from the browser to an external synth!
Make a MIDI chat room with WebRTC and send notes to your friends without server-side code!