This is an open-source quiz application. The current dataset is for world capitals, but it can also be easily adapted to work with language vocabulary learning as well, or other paired, categorized data that is worth learning.
You can download the app from Google Play: https://play.google.com/store/apps/details?id=net.xenotropic.quizznworldcap
You can also see a version of the app being used with a Spanish-language dataset in the Quizz'n Spanish application: https://play.google.com/store/apps/details?id=net.xenotropic.flashcards
The format of the quiz data can be seen in "res\raw\wordpairs". It is a CSV file, where the first two columns are the pair of associated datapoints (country/capital; or word/foreign-word), and the third column is the category.
If you create a deriviative work based on this, please bear in mind that you will also have to license it under the GPL. Please maintain the pop-up EULA notice on first install with credits/copyrights, GPL, limitation of liability, and implied warranty waiver.
If you have any questions about the application or how you can use it, please email me at firstname.lastname@example.org.