Clubs is a feature that was once available on Duolingo's mobile application. It was created for the purpose of learners being able to "connect online and stay motivated". This was accomplished by joining a small group that competes for the highest XP score, while also encouraging one another with an emoji-based chat system.
The limit for a club group was fifty members. Any user could make their own club or join someone else's. You would join someone's club by typing in a six-digit code provided by the club admin, or by searching through a list of open clubs. The club admin made decisions regarding who can join and whether they can accept new applications to the club or choose an avatar for the club. You could join a club for each language that you were taking.
The arrival of the Leaderboards feature led to the discontinuation of Clubs.