If you enjoy flashcard-style learning, try out Brainscape. Based on the claim that individuals can double their learning speed by using flashcards, this tool paces the repetition of each concept, so users retain knowledge more effectively. Rate how well you know each concept, and Brainscape will determine the right time to give you another quiz. It's free to create, share, and finduser-generated flashcards.

Brainscape partners with top publishers, schools, and educators to create flashcards for subjects as diverse as foreign languages, the Medical College Admission Test, music theory, Advanced Placement exams, Series 7 prep, and sports trivia. Students, professors, teachers, and businesses around the world have created more than 1 million subjects that are available via search. Users can also easily create multimedia flashcards both online and within the app itself, as well as share decks with classmates and collaboratively develop content together.

A subscription isn't required to use Brainscape, but it does give users access to unlimited premium content; features such as bookmarks, browse mode, card reversibility; and flashcard creation without ads.