OTOONE is a free and innovative musical instrument (synthesizer) designed for both fun and education purposes. It is an Android-based program that is completely free and requires no internet access. With its simple operation, quick response, multi-touch, reverb, and volume control features, users can create music with ease.

The program's interface is user-friendly, with a green line representing the sound of "C major (C D E F...)" and a yellow line representing the sound of "D major." The musical notes are arranged from left to right, with "C, C#, D, D#, E, F..." and from down to up for octave change. Although practice is required to master the instrument, users can enjoy creating music with OTOONE for both fun and educational purposes.