I recently released an interactive metronome training app called TempoTutor-Toon that focuses more on the fun aspect but has several forms of audio and visual feedback so it can be an effective trainer. I created it for myself and my (adult) daughters who have benefited from using it. I may develop more variants if there is demand, but the first one was "toon" themed to help appeal to a wider audience. I implemented heads-up indicators, on-screen statistics, detailed statistics, stereo audio (indicates if you are early, late, or on time), and even a pink noise option to help with focus. Check out more details here: https://www.cardilloscreations.com/app/tempo-tutor-toon/ For the record, this type of app isn't as easy to develop as you might think at first glance. First of all, smartphones cannot really produce anywhere near the precision that is possible with specialized equipment. Most are lucky to be able to support 60fps, which is a timer granularity of roughly 16.67ms, and then you still have to account for other processing hiccups, touch propagation, etc. You also have to be careful about how you detect the time difference and periodic timer frequency to avoid clock skew. System timers do not fire precisely - so you need another way. I dealt with this and was able to achieve fairly accurate timing and measurements (as much as possible with a 60fps max). Then, if you solve timing and clock skew problem, you need to be sure that the statistics and other features provide interactive feedback that's accurate enough to provide useful feedback during training. Ultimately, I focused on creating a fun design with key features that are essential to using it as an effective interactive metronome trainer.