On paper I like matrix, or prosody (xmpp/jabber) with extensions (ditto irc + logging bots etc).

But after looking a bit at rocket.chat along with the api - it's hard to recommend something else as a self-hosted, open slack alternative.

I'm not enthusiastic about the stack/mongodb dep - but boy is the api nice and documented, and their docker-compose a joy to get started with:

https://rocket.chat/docs/installation/docker-containers/dock...

https://rocket.chat/docs/developer-guides/rest-api/

[ed: oh, and there's a hosted option and you can pay if you want. I think that's also a big plus]

Out of curiosity, have you looked at Mattermost? How does it compare? About three years ago when open source Slack alternatives were starting to hit, Mattermost and Rocket.Chat were the top options. GitLab even ended up bundling Mattermost with their Omnibus installer (and were going to bundle Rocket.Chat as well, had they made it possible to support Postgres, but I don't think that's the plan any longer).

Not really. I'd prefer matrix (open protocol, federated) - but I seem to recall after reluctantly accepting that rc is a great product, I had a look.

And that bundling code inside a mysql container felt like it fell well short of the simple rc setup of db+app via docker compose...

https://github.com/mattermost/mattermost-docker-preview/blob...