Spacebar.chat (or github here) is meant to be a drop-in replacement with support for discord bots, but it has been super alpha the few times I’ve tried it. Haven’t checked in for a few months though!

(Edit: yeah I just checked and spacebar is still very much a work in progress. Looks extremely promising though!! It seems there are devs posting updates on the main spacebar instance, which is cool)

Rocket.chat also has a self hostable option, but I don’t recall that one being super great either.