It must be possible to practice these things on a smartphone! That was the idea a while back. After quite a bit of thinking, trying, programming, and testing, we can now offer our solution.
VOR Tracker is a real simulation, so you will find no multiple choice questions or abstract explanations. You can actually practice holding patterns and radial interceptions in real time, using either an RMI or HSI.
Yesterday, the iOS App was released in the App Store. The Android version is soon to follow.