Try Duolingo's TinyCards. They released the app recently and it helps you with memorization while you play games. If you just want raw words to put on flashcards, on the desktop site there is a little widget on the top left beside the home widget labeled "Words." It gives you a list of all of the words you have learned, when you last practiced them, and how weak you are with each word. It's really helpful!

Just go to this post . https://www.duolingo.com/comment/24995196 Hope it helps ;)