Don’t go into slack or discord unless you are able to access every possible chat room. People are weird, neighbors are wierded, neighbors online are absolutely toxic. Theonly alternative is that you have access of all chat logs in the app. Setting up mattermost on a vps would work, but I think there are better options for what app to use. Funny enough Next loud can do everything you want it to do, including slack-lile chat rooms, VoIP, email, contact management, cloud storage, web portal, and you still have access to the logs (in case something wrong happens).