Discord is a great tool for gaming communities and other similar groups. If you might otherwise be using group chats on Facebook, or Skype, Twitter, Ventrilo, Mumble, or Teamspeak then sure, switching to Discord is a no-brainer. Do it today; there's a reason so many gaming communities have embraced it so quickly and thoroughly; it's much better than the alternatives.

It's also great for creative writing groups, clubs, hobby groups...great tool for casual organisation of 3-50 people where most of your time is going to be spend casually chatting and linking images and posting jokes. It's also much better for creating ephemeral groups.

But I'm not really sure I think it works for open source projects. "Better than Slack" is setting the bar really low; Slack was a bad solution for this as well. In particular I'm concerned by: 1) Walled garden 2) uncertain corporate future 3) lack of public, searchable logs 4) lack of interoperability and federation 5) lack of deep links into archives 6) barrier to new members.

Reactiflux on Slack was a poor experience; they outgrew Slack and were forced to jump to Discord and...it's still a poor experience. It's like hitting yourself on the hand with a hammer, realising it hurts, so getting a different hammer. This isn't progress. I'm not sure it's worse, so sure, if you're already on Slack and you want more of the same then sure, switch to Discord. But maybe first think about alternatives that aren't "the same thing I already have with a dark theme"?