Zorbi - Spaced-Repetition Flashcards - Other tools are built by boomers, Zorbi is built by students.
Mochi - Write notes and flashcards with Markdown and study them with spaced repetition.
Yak Tack - remember. words.
Harken - Flashcard app using smart repetition to improve your memory
CleverDeck - Learn languages more efficiently with spaced repetition
FlipToMind - Space repetition app to help you remember everything