Discord is growing rapidly for a lot of use-cases, including professional uses. There are a few slack groups out there but they seem few and far between without very many members. Unless it's a paid version they don't have much of a history to them (90 day limit) to see prior messages. They are also invite-only so you have to know about them or someone in them to get in.

We thought we would try to create a Discord server instead, it is open, searchable, and possible to keep more organized even as a free option: https://discord.gg/gb7TbAdwzn