Brilliant.org seems to copy Duolingo. They have a day streak system and leaderboards. Not good.
Fun fact: I have a Duolingo streak of 1992 days right now.
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@phillipp when the app is good (Duolingo is) the streak system and social features are great ways to reduce churn. I can’t even think of trying another app because I have my whole extended family on Duolingo and obviously I’ve been working hard for my 2100+!