For certain activities, you unlock Achievement Badges. Some of these are Inner Circle, Sharpshooter, Big Spender, Overachiever, Overtime, Friendlt, Wildfire and Champion.

Each badge has 3 levels that you progressively unlock.

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Duolingo

Onboarding
Top level tabs
App Store screenshots
2019 redesign
Duolingo Plus
App icon change
Learning experience
Asking for notiification permissions during onboarding
Duolingo Clubs
Change or add language
Gamification: Streak, Lives and Gems
Gamification memes
Create profile

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Gamification

Blitz Buy gamification
Card Gamification: Category Cards
Converting steps to coins
Transfer coins