Duolingo's addictive scoreboards

Duolingo teaches users new languages in short, interactive lessons that require neither teacher nor a traditional textbook. The innovative app has gamified language learning with various incentives that keep users active and engaged in the long run.

Why this is really good UX:

• Every time users open the app, they have a whole array of numbers, stats, and other visual incentives goading them to complete more lessons and improve their performance.
• By tracking progress and success through different metrics, the app caters to a whole variety of learning styles and motivational profiles. The fluency percentage, for example, (which can go on users' LinkedIn profiles) drives long-term commitment, while daily goals and charts incentivize short-term success. A leaderboard fuels competitive types who enjoy competing against friends.
• Taking a page from the gamer's handbook, the app also rewards lesson completion with gems that users can  exchange for “power-ups,” timed practice, or bonus skills. Collecting gems to buy these add-ons  motivates daily engagement.
• The wide variety of progress tracking and motivation options lets users build personalized language programs based on how they learn best.