Smartr

Smartr is a learning tool and study aid that allows you to create stacks of cards with information that you want to learn, and then study them like flashcards.

Only these flashcards are smartr: In your study sessions Smartr quizzes you on cards that are carefully selected for you based on your past performance, what you need to study, and when.
When creating a new stack of cards, you can choose to have one stack per subject, class, book, or chapter of whatever it is you are studying. You can also choose each card type within the stack. Some example card types include "Question and Answer", "Definition", "Picture Identification", "Japanese Kanji Vocabulary."
If you'd like to try out Smartr Lite for free, you can start building your own stacks using up to a maximum of 100 cards.