Connect your piano via MIDI with the smartphone and start the app. Now you can choose the screen:
Legato Training
See how you play the piano. The vertical bars are red when the tones overlap (legato). They are green when between the tones is a gap (staccato). The white bar at the bottom and at the top indicate how "simultaneously" you hit multiple tones (below) and release (above).
Try to play so that no bars appear.
Chords
Press a chord and see the chord name.
This application is made using libgdx and makes use of the USB-MIDI-Driver library by kshoji. The source code is here: https://github.com/Meisterschueler/meisterschueler-gdx