Leitner app is designed to help people memorize flashcards bearing information as words or numbers, on either or both sides. One writes a question on a card and an answer overleaf. Flashcards can bear vocabulary, historical dates, formulas or any subject matter that can be learned via a question and answer format. This app using Leitner system which is a widely used method to efficiently use flashcards that was proposed by the German science journalist Sebastian Leitner in the 1970s. It is a simple implementation of the principle of spaced repetition, where cards are reviewed at increasing interval.