Auto-assign a hoisted role while a member is playing a game or using an app (for example, a "Playing ARK" role, or a "Listening to Spotify" role). Packet removes it shortly after they stop, so the member list groups people by what they're doing.
A rule can match an activity by its name (the name contains your text, is exactly your text, or fits a pattern), by the application id Discord reports for a game or app, by its type (Playing, Listening, Watching, Streaming or Competing), or a mix. A rule can also post a short "now playing" message in a channel you pick when a member gets the role. It posts at most once an hour for each member and rule, and it pings nobody.
Hoisted roles and the member list. Discord lists a member under their highest hoisted role. An activity role only groups its players above everyone else when it sits higher in your role order than their other hoisted roles. A member who also has a higher hoisted role, such as a staff role, stays under that one while they play. (Configure → Activity roles.)