Semitone is a tool for musicians that includes a tuner, a metronome, and a piano. The design is as simple and easy-to-use as possible while implementing many useful details, such as: * an option to set A4 pitch for alternative tunings * the ability to manually set strong beats on the metronome * dynamic resizing of the piano keyboard Semitone is free, open-source software. The source code is available on GitHub under the GPLv3: https://github.com/tckmn/semitone/