Brainscape is an excellent FREE iOS app/site for flashcards. Flashcards on Steroids…….Over 800 academic studies have proven the efficiency of spaced repetition.
But nobody has ever made it as personalized as Brainscape. Brainscape's innovative "smart" flashcards works in timed intervals that a user rates on a scale of 1 to 5. Brainscape then used an adaptive learning algorithm to differentiate instruction and display the flashcards that need more focus on. This is a great way to learn difficult subjects and break down difficult concepts.