> You still haven't explained why e.g. Zulip
I think that Zulip is a good service and AFAIK Zulip is the OSS project based on Python.
But I think that such communication tools should be evaluated not only technology side but also on how people feel familiar with UI/UX.
I don't want to evaluate the UI/UX accessibility of Zulip is good or bad but it's the issue of how people feel familiar.
This phenomenon also occurs in other common (non-business) messengers.
(WhatsApp, Facebook Messenger, etc..)
You can observe that there is no single monopoly messenger which concurs worldwide.
The list of tools that I suggested is based on my personal observation which is normally used in tech companies.
If people feel familiar and such things can address people's productivity I think that that's a good reason to choose.