Slack is a widely-used chat application. We are moving toward using it for seamless communication across the CS Department and the CST generally.
Slack advises that you can't have "too many channels". Channels should be based on topics not just groups of people.
Fortunately, adding channels is easy: in the right sidebar, find the section header "Channels" and click the neighboring "+".
Slack has deprecated the webhook integration tool we had previously used for GitLab integrations. We're now following their supported mechanism for handling it. You may use this as a model for future Slack apps.
The free Slack version supports up to ten apps and integrations.
We have one app, "GitLab Notifications", which we are gradually integrating into a subset of our channels. See more about it at this page.