Info commands
The lookups people expect: user, server, role, channel, avatar.
What there is
/userinfo /serverinfo /roleinfo /channelinfo /avatar /banner /botinfo. No setup needed; on by default.
Worth knowing
Every reply is private to whoever ran the command. A lookup is for the person asking, and answering publicly turns “when did they join” into an accusation in front of the channel.
You can restrict looking other people up to moderators. Members can always look up themselves.