Credits
Piano sound
The piano sound is from the FluidR3 General MIDI soundfont by Frank Wen, as rendered to MP3 by the midi-js-soundfonts project (Benjamin Gleitzman). It is used under the Creative Commons Attribution 3.0 licence. The app uses a selection of its notes in MP3 form.
Demo piece
Ode to Joy by Ludwig van Beethoven (public domain), in a simple arrangement written for this app.