I mainly hang out in two Slack communities, both quite high-volume. The first one is public but regional (not in English), the other one is invite-only but quite big.
For people who want a nice place to hang out online, I can warmly recommend starting a Slack (”tenant”?). I’m kinda surprised that more people don’t try this. Mattermost or Discord might work too, but IMHO Slack still has the best UI for this. (The shortened retention sucks of course, but it’s still very useful.)
My feeling is that Discord is taking over Slack for a simple reason: it's easier for "community contributions".
In Slack, if you want to keep the history (which most people seem to really, really need for some reason I don't get), the owner of the community needs to pay (a lot).
On Discord, the community members seem to be able to make some kind of contributions as a "donation". Not sure exactly how it works, but I have seen a few open source communities move to Discord for this reason.
Yeah that might be a good selling point for Discord. So far I haven’t really felt at home in Discord’s UI paradigm, but I also haven’t found any ”must-have” communities there either (for my tastes).
