Mimicking Duolingo's fun and interactive system, and maybe add "invite/challange a friend" feature such as: Streak competition Where, progress is competing in daily quest to get a streaks, (separate from the general daily streaks). Pages being read Where, we just read as much as possible in a date range of the challange Memorization being reviewed The financial and economy. Make the "challange a friend" cost a <X amount> via in-app currency make it cheap to enter, and the winner gets to keep half of the X% of the loser. Or something to penalize the lower and in-game reward to the winner. Premium users gets free access to these challenges and its opponents gets cheaper entrance cost.