This simple app helps you learn the layout of the piano keyboard and guitar/bass fretboard and how they relate to each other. Press any piano key or tap a guitar string on any fret and you will see the corresponding key/fret on another instrument.
For guitar/bass it also shows where the same note on other strings is located.
Click/tap once to highlight the note and click/tap it again to turn off. The same notes have the same color but notes in higher octaves have higher lightness.
This app is open-source, made by axln. For more info, please visit the app's page at GitHub.