> Mattermost, Zulip and Rocketchat I have the least experience with; they all seem to be very popular with small groups of users but are complex to install and

> Mattermost, Zulip and Rocketchat I have the least experience with; they all seem to be very popular with small groups of users but are complex to install and have very few clients. At least for Mattermost I have to disagree with the "complex to install". All you need is a sql database (MySQL/MariaDB or Postgres), for production you then also should put a reverse proxy in front. With "very few clients" you are referring to client software, correct?