PitchPipe is an Android app I wrote for practice; it's the first app I wrote that doesn't involve displaying "Hello, world".
The idea is that if you're out somewhere with a group of choral singers but don't have a piano handy, you can use this to give the singers their pitches.
Some of the code is adapted from code written by Kevin Boone; see http://kevinboone.net/javamidi.html. Please see http://kevinboone.net/download_policy.html for his policy on using his work.
This repo is set up as an Eclipse project. It should be possible to import this directly into Eclipse and build it, if you've configured your Eclipse to work with Android projects. If not, my apologies; I'm new at this. You may have to configure the build path. Minimum Android API is level 11.
Well, not too many yet. But there's a Stop button to stop a chord that's currently playing, and a Replay to replay the last chord. The menu has "Select instrument" so that you can change the instrument (MIDI program) used to play the notes.
I've gotten this to work on a Samsung Galaxy Note 3, which has a large display, for a phone. I have not tested it on smaller displays. It is likely that a smaller display will not support the number of buttons the app currently displays, and the UI will need to be different. This is something I'm planning to address.