I have refreshed my Installer and found an app called Anki Flashcards. It says in the description that Anki is a program designed to help you remember facts (such as word and phrases in a foreign language) as easily, quckly and efficiently as possible.

It apparantly asks the user to rate his or her knowledge on a 5-point scale and the scale determines how long it will be before the flashcard reappears. The effect is that difficult flashcards will appear frequently, and the easier ones fall to the back.

It does need an an Anki account though and I'm not sure if it's free or not. Try and find out.