Tonaly is a music app for iOS, iPadOS, and macOS that focuses on key-based exploration of harmony for songwriters and musicians. Instead of presenting music theory in abstract terms, Tonaly structures chords and scales around musical keys, enabling users to understand and apply harmonic relationships in a practical way.

The app can be used for songwriting without a physical instrument, making it suitable for developing ideas on the go or away from the studio. Scales and chords are displayed visually on integrated instruments such as piano, guitar, bass, ukulele, and orchestral string instruments, allowing users to explore tonal material directly within the app.

Tonaly is aimed at musicians without formal music theory training as well as experienced songwriters who want a streamlined, key-centered workflow for composing and harmonic exploration.