Create quizzes/tests and practice it in a number of ways (currently two, multi-choice and flashcards). The idea is to make learning social. All quizzes are public by default, everyone can contribute by adding explanation or comment. Also, new feature 'requiz' makes it possible to create quizzes from already existing questions by simply 'requizzing' it. Android and iOS apps also available, however not all features yet supported.
Quizzn is still a young project, but it is a free educational tool that can make studying easier.
We follow two trends: fun - create new ways to practice subjects; social - make it easy to connect and share knowledge.