https://cloud.sagemath.com deploys Jupyter into a multi-user environment. It's used by hundreds of courses for teaching across the world. Our Jupyter deployment also supports realtime synchronization (multiple people editing at once like Google docs) and recording of the complete history of the document. I've also spent the last few weeks on a complete rewrite of Jupyter from scratch using React to provide more robust realtime sync support, faster startup, and better integration with the rest of our platform; this rewrite is of course not live yet.