Recall improves your long term memory by testing you on your flashcards less often when you get them right, and more often when you get them wrong.
Recall is based on the psychology of spaced repetition and the Leitner system that says that the harder it is to "recall" a memory, the longer it will last in your memory before you forget it the next time. Recall shows you flashcards at the right time to make recalling the answer more difficult, improving your retention.
Automatic card shuffler to prevent memorising cards in a particular order.
Ability to attach images to cards.
Setting to review flashcards from back-to-front or front-to-back, perfect for learning vocabulary of foreign languages where you would want to memorise the word from from your native language to the foreign language, and vice versa.
Ability to share decks with friends or students.
A setting to use the Sans Forgetica font to improve memorisation.