i have not followed the slack replacement discussion very closely, but have you folks considered http://www.potato.network/? Its client is written in cljs/react, the server is in common lisp.

@hans: this is the first time I've heard of Potato chat, thanks. Have you used it? What else do you know about it? Are any communities like ours using it successfully?

@meow: I think it is currently used in a commercial setting for one team. The guy who wrote it is a long term Common Lisp programmer. I don't know much more than that.

@meow: It is completely open source, which I find kind of appealing.