… are made for workgroups (“groupware”) and can be seen as open source alternatives to “Slack” (“Slack is your digital office - revolutionize the way you work with one central place for everyone and everything you need for your daily work.”). What they all have in common is that interfaces are available so that other systems can be integrated into the internal workflow.
As a rule, these exist in both an open-source and a paid enterprise variant with professional support. The business packages offer additional features such as support for high availability.
Cross-reference: System comparison
„An open network for secure, decentralized communication“
Chat and work via distributed database (a lá Git). Split between Matrix.org (protocol development) and Element.io (distribution and hosting). Matrix compares itself (external) not with other team messengers, but with IRC, XMPP, Trillian and Pidgin.
Examples of educational use: Uni Bochum (external), TU Dortmund (external), Uni Hannover (external), Uni Insbruck (external)
More examples: BWI (Bundeswehr) (external), French government (Tchap) (external), German health care (TI-Messenger) (external), Handmade Seattle (external)
„Make your work flow”
Examples for educational use are Uni Kaiserslautern (external) Uni Mainz (external), FH Münster (external), WWU Münster (external), The University Of British Columbia (external).
More examples (like Bosch, DuckDuckGo, NASA, Nasdaq, Samsung, …) can be found on the site of Mattermost (external).
„The world’s largest open source communications platform. Own your data, customize anything, integrate everything.“
In the documentation of Rocket.Chat it is stated that a federation is possible, however (as of 05/2022) it is disadvised from productive use. Here is in the configuration settings for federation (screen shot) the warning:
“Federation support is a work in progress. Federation support is a work in progress. Use on production system is not recommended at this time.”
Source (English): https://docs.rocket.chat/guides/administrator-guides/federation (external)
Examples of use: Uni Bremen (external), Heinrich-Heine-Universität Düsseldorf (external), Hochschule Koblenz (external),
Uni Köln (external), Uni Regensburg (external)
More examples (like DB, VW, Audi, …) can be found on the page of Rocket.Chat (external).
„Chat for distributed teams.“
This Teammessenger is also made for working in distributed groups and “threads”. Zulip explicitly advertises that the paid variant funds the open-source version. Other services such as Dropbox, email, GitHub, GitLab, GoogleCalender, Matrix, Youtube and many more can be integrated and it is possible to run your own Zulip server. Examples of educational use include University of Munich (external) and University of San Diego (external).
Compared to the open source competitors Mattermost or Rocket.Chat, Zulip offers free hosting on Zulip servers in addition to the option of self-hosting.
Comment on Zulip:
The most important difference, in my opinion, between Zulip and most of the other popular chat systems is their conversation model. With most systems, like Slack, Matrix or even XMPP, conversations are separated into channels, rooms or chat rooms respectively. For some of the newer chat systems, threads have been added to conversations as an after thought, but in Zulip, threading was an initial design feature so the system was built to support threading, in a similar way to email.
Source: https://mailarchive.ietf.org/arch/msg/tools-discuss/WAvOx6dkPKu-UanUYtzeNhGjydg/ (external)
More detailed description: blog.novatrend.ch (external)
Source code: https://zulip.readthedocs.io/en/stable/production/install.html (external)
Interface: https://zulip.com/api (external)
Project page: https://zulipchat.com (external; unfortunately only English)