The top level tabs have roughly stayed the same while the visual style has been tweaked to be cleaner and the owl has been redrawn.

The Clubs feature is being A/B tested against the Leaderboards tab (and some users aren't happy about it: Petition to save Clubs)

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Duolingo

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

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Content Screens

Flashcards screen
Top level tabs
Hotel page
Login and top level tabs