Simple ad-free quiz app to learn the Circle of Fifths, Tonic-Subdominant-Dominant algebras and key signatures.

Features:
- Tonic-Subdominant-Dominang algebra quiz - determine the correct chord for given harmonic function.
- Key quiz - determine scale for given flats and sharps .
- Key quiz - determine flats and sharps for a given scale.
- Reimplementation of Alain Benbassat's ear training method, also known as FET / Functional Ear Trainer. (Including church mods, last-to-next question mode and other advanced features unavailable in other implementations.)
- Simple progression trainer. (Reimplementation of ChordProg degree based chord ear trainer.)
- Brief explanation of music theory.