The Leitner system is a widely used method of efficiently using flashcard that was proposed by the German science journalist Sebastian Leitner in the 1970s. It is a simple implementation of the principle of spaced repetition , where cards are reviewed at increasing interval.
having multple groups
have groups in multiple folders
have packages for download( 504,1100,first ,second , third and forth grade in high school )
You can have this box everywhere and everytime.