I use Flashcards Deluxe for an adult German class I'm taking; myself and another student collaborate on creating the cards together. You can do it on the phone, or enter them into a spreadsheet, and use their website (free) to convert the spreadsheet to cards; the rest of our class can download them for free.
They have a Lite version so you can check it out. It's got a lot of features, you just have to spend a little time experimenting.