Quiz apps get so repetitive after a while, with the same questions repeated over and over again. My friends and I were about to give up until we found a site with actually engaging quizzes. They have five difficulty levels, and the expert ones are brutal: less than 20% of people answer them correctly. You get more points for harder questions, and you can compare your scores with others. The topics are far more varied, and you can filter by topic or difficulty to find exactly what you’re looking for.