Another alternative you could consider is Zulip. Unlike Element/Matrix it does not support E2EE (at least as far as I know) but it is fully open source software with a pretty active community. Also unlike Mattermost they provide free cloud hosting and don't lock certain features behind non-OSS enterprise versions.
Zulip/Mattermost are probably a bit more full featured than Matrix/Element but Matrix/Element are built around E2EE and federation.
FWIW Element/Matrix is the only one of these identified on the site connected to this subreddit: https://privacyguides.org/software/real-time-communication/
I have used all of them, deploying them and all (and still use mattermost in one org i'm part of).
I must say that Zulip has contributed to our organization much more than one would expect, by providing a tool not only to chat, but also to help us organize conversations in a productive way.
Chrck out Zulip. Unlike Mattermost, it can he used for free on the cloud and you can also self host it. It has a unique system of topics where each message in a stream can have a topic. This really reduces a lot of clutter in streams.
Zulip also has bots and integrations for various services. Plus it integrates with IFTTT and Zapyer to provide more.
I think iyou should definitely have a look at it.
Just throwing this out there, Slack is poison and if you’re in a position to not use it, I strongly recommend Zulip instead. It has better support for threads, is fully open source and can be self hosted, their own hosted version is free for academics and open source communities, it has real markdown support, and real LaTeX support both inline and as blocks without having to use extensions.
There's the searchable archive at Clojurians Zulip. (Good summary of why Zulip is a good fit for communities.)
Zulip is about to release public streams, which allow for discussions to show up in Google/DDG searches.
I work on Zulip and I'm sad to hear that! I personally use the app every day and other comments are more consistent with our sense of the app's development state. (Being far from perfect is why the mobile app is also one of the main places our paid engineering team is spending its time).
Bug reports from users are extremely helpful; the reality of mobile development for a complex app like Zulip is that there are a lot of potential problems that only affect particular configurations / devices / workflows / organization data sets.
So I'd very much appreciate it if you stopped by https://zulip.com/developer-community/ and batch-reported the things you've noticed in #mobile.
With the caveat that no tool will fix communication and culture by itself, this is a great post in pointing people in the right direction.
Really heartened to see several of the suggested tools are libre software also offered as a service.
Also wanted to point out Zulip, which we chose for all the reasons that Twist touts itself, but (in addition to us finding Zulip first) has the added benefit of being libre software, open source, and so self-hostable if needed.
The first lines of the install script configure the PPA that contains those packages:
wget -O /root/zulip-ppa.asc https://zulip.com/dist/keys/zulip-ppa.asc apt-key add /root/zulip-ppa.asc cat >/etc/apt/sources.list.d/zulip.list <<EOF deb http://ppa.launchpad.net/tabbott/zulip/ubuntu trusty main deb-src http://ppa.launchpad.net/tabbott/zulip/ubuntu trusty main EOF
So I'm not sure why this wouldn't be working for you -- can you send a bug report to with your terminal log?