I was recently considering writing a MUD-like multiplayer text adventure game in Clojure and Clojurescript that used RethinkDB change feeds over WebSockets (through the excellent sente library).

Not quite what you're asking for though.

Maybe if I get some time in the coming weeks I'll give it a shot.

>Not quite what you're asking for though.

WebSockets support, so that plain Javascript in a browser can connect to the server without having to wrap in node-webkit or use Java or whatever.

You can use websockify to bridge the gap: https://github.com/kanaka/websockify

That would be slick. However I think Slack keeping up with nice clients on every platform imaginable is a nice way to piggyback.