Screenshots of Open Source Alternatives to Slack that I tested
This was the shortlist of what I tested out in practice in the end. I'm actually using Riot.im the most mainly because I'm on actual discussion forums relating to Mastodon. But Riot.im does not have threaded discussions so it came pretty well much down to Rocket.chat (more modern look) and Zulip. I'm actually leaning more towards Rocket.chat as it was a super easy installation on my virtual server and is doing all the basics I need.
I also included screenshots of Friendica (Facebook alternative) and Mastodon (Twitter alternative) juts for those who have never seen what they look like in practice. Both are federated services with no paid advertising or passing on of your private data to 3rd parties.
See the album of screenshots at https://flic.kr/s/aHsmfAZH2a