When I set out to build a new realtime chat app, I explored various options and landed on wamp/crossbar.io as a potential choice. This was a few years ago but at the time it seemed promising, reasonably well-documented, and had both python and js clients.

One problem was whether it would support horizontal scaling if you needed to expand beyond a single node, and at the time they were "working" on a global/cross router but it wasn't ready. It's a hard problem to solve and one that may not be required for many use cases. I'm not sure if they delivered it but I ended up going with mqtt instead.

To piggyback on another commenter, their javascript library did feel a bit bloated/dated, but I also got the impression a few of the people were juggling a lot of related projects and maybe there wasn't enough of a community. Haven't checked back recently.

In any case, the project is still impressive, has some dedicated people behind it, and could be a great solution to add websockets to a project.