To learn using flashcards was quite a simple and far-from-exciting experience for me. Not more.
Mental Case impressed me since the very first time I ran it. This app put the flashcards in a whole new level. It combines a beautiful, well-polished interface with a number of excellent features.
Firstly, you do not need to leave Mental Case to download card sets (stacks) from the thousands available for free on Quizlet and FlashcardExpress. Stacks can be grouped in cases and freely ordered.
In second place, you are not limited to the traditional two-sided cards. Mental Case 2.x can create and handle cards with multiple facets, a convenient resource to complex matters.
Card editing allow user to change fonts and colors, insert images and audio and even apply stack-wide format using templates. For each stack you can define a number of controls regarding the way Mental Case will exhibit the cards.
A very nice feature is the Learning Schedule option, what lets user to choose between five patterns. Mental Case will keep track of your studies and can handle the card exhibition considering a target deadline or a spaced repetition (the "long-term learning", based on an algorithm). The cards you gave wrong answers or did mark with "wrong" will be showed again after a while until you get it correctly.
As small pluses Mental Case groups the recently studied and added cards, the recent wrong answers, the cards not linked to any stack or the ones due to study.
Although expensive for a flashcard tool, Mental Case offers much more than any other app I tried. It can be improved in some points, as quicker card edition or more controls when searching though the stacks available on the web. Anyway, the app is quite impressive right now and a real pleasure to use.