Slack's (hypothetically) down for the day again. What's your backup?

Question

With the recent Slack outage, I've been thinking about back-up team-wide communication systems.What would your preferred system be to revert to? Keep in mind that whatever you pick, you're going to be paying for, or putting in the effort to host.

HDMI_Cable · Accepted Answer

This isn't for work, but I do know that a lot of schools (study groups, clubs, etc...) are using discord, because they have a lot of the same features, and are relatable to anyone under the age of 25.