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

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

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Content Screens

Top level tabs
Interactive News Experience
Recipe page
Top level tabs