Vocabagility is more than a flashcard system, it's a method. Cards are selected and shuffled, one side is shown. Give an answer, did you get it right? Move on. As quick and easy as using a pack of real cards in your pocket.
The system also encourages you to invent an amusing mental image linking the question and answer (Visualization and Association)
Cards that you're not certain about have a greater probability of being shown.
This is an effective system for learning vocabulary / phrases for any language but could be used for learning other things too.
Download Vocabagility for Mac for free here.