An app that allows you to play notes on different instruments, record those notes and play them back.

This app has a basic quiz, or if you select the custom questions box, it gets questions and answers from an api where you can be quizzed on many different things.

An app that asks you to add up different numbers, then tells you if you are right or not, after you can get a new selection of numbers. 

An app where you can draw on images with the tools provided.