Brilliant

The app takes another approach to learning, one that doesn’t require you to go through lectures and watch long videos. Brilliant has lots of quizzes which make it fun to learn new things about math, science, engineering and many other topics.
 
Each section is divided into many quizzes and you can learn from students, Olympiads, researchers and professionals. Each problem comes with steps for solving it and the app provides you with a selection of problems daily. In addition, you can ask your questions to the community and get answers fast. The app tracks your progress with solving problems and you can check out the most popular topics, which are probability, number theory, computer science, logic and more.