Google+/features/Community

"Communities" were a feature on Google+ which provided functionality similar to a Facebook group or even a Discord or Slack server.

Any Community had the following features:

• shared space -- any member can post to it
• opt-in -- you decide which ones to join (or request to join, if approval is required), and you can leave anytime
• moderated -- admins can boot people out
• privacy options -- a Community can be
  • invite-only, join-on-admin-approval, or join-immediately-on-request
  • publicly-viewable or members-only
• categories (limited functionality, though)

Google+ deployed circles quite some time before communities were deployed.