Zöff
Live music playlist sharing — everyone in the room adds to one queue and hears the same thing at the same time.
Zöff is a shared music service: several people come together and build one playlist, and everyone hears the same track at the same moment. Anyone can add something, and the room decides what stays.
The interesting problem is synchronisation — playback position, queue changes and votes all have to propagate to every client in real time, and stay correct when people join partway through.
The original ran at zoff.no; the current app lives at zoff.me.
Tech: Node.js, MongoDB, Socket.IO, YouTube API