I would like to voice that there are people who find slack not very good for very active communities.

On the one hand it's a real-time chat, on the other hand it always feels like you are missing out if you are only opening the app now. But you also can't just leave a message and come back later because the scrolling is awful and everyone has probably just moved on from that conversation.

I really prefer IRC + log and something like reddit/mailing lists over slack and have recently stopped interacting with a community that have all moved to slack.