We provide our full Zulip Cloud Standard paid plan for free to open source projects (and various other worthy causes!). We also prioritize and build features specifically because OSS projects asked for them:
https://zulip.com/for/open-source/
Hundreds of open source projects, including Rust, Julia, MariaDB, and Clojure, use Zulip as their team chat platform. We often hear from large open source projects that they substantially prefer Zulip's topic-based model to the user experience in Discord or Slack, or that they found it made their open source community work. See for example these tweets from the last few weeks:
* https://twitter.com/mojavelinux/status/1409702273400201217
* https://twitter.com/ornicar/status/1412672302601457664
Also in contrast with open core products like Mattermost, Zulip is proudly 100% open source software. You can learn a bit more about Zulip's open source model here:
https://blog.zulip.com/2021/04/28/why-zulip-is-on-github-spo...
Personally, i find Rocket.Chat ( https://rocket.chat/ ) to be simple enough to set up in a Docker container and have running as a passable alternative to Slack/Discord. There are downloadable clients as well. The only real downside I've seen is somewhat bad support for calls because their WebRTC implementation is still new and integrating with Big blue button or whatever else they offered is hard.
Does matrix / someone else solve it? How?