Here are my favorite Chinese Mandarin learning apps.
StickyStudy
This $4 app is easily the best Flashcard function out there. The Leitner Study Method algorithm works beautifully to introduce, rehearse and re-enforce vocabulary. The HSK levels are complete and well edited. Very nice and the best way to build your Chinese Mandarin vocabulary. Comes . . . → Read More: My Favorite Chinese Mandarin Learning Apps