I use Anki, after been inspired by the excellent testimonial of Michael Nielsen of Y Combinator research. I use also one Anki deck.

I have an idea for a new app: Anki with audio. Suppose, you are driving in your car and start the Anki-audio app (this has not been developped yet). Anki-audio playes the first question over the car audio speakers and pauses. You give the answer out loud. Anki-audio, noticing that you have said something, playes the right answer. Then it asks you: how hard or easy was this? You answer this question with standard words, like for instance hard or easy. This way, Anki only has to be able to understand these standard replies.