Just yesterday I was musing that if I were King of the (World|Company) I'd want an open-source Slack-alike that I could just drop into the Cloud of my choice and operate entirely within my private network, subject to my own access control just like other internal services, and with full access to all message histories in whatever database-like thing it uses in its Cloud. Sure, I'd still have a SPOF but it's game over anyway if my Cloud goes dark.

Is there such a project, and if so does it have any traction in the real world?

(Oh and ditto for every damn thing Atlassian owns. Yikes.)