Clef

Clef is an iPhone and iPad app for adult beginners and returning players who can find middle C but still decode notes slowly. It trains reading and keyboard skills with short drills across 15 tracks, from treble, bass and ledger notes to intervals, key signatures, triads, scales and arpeggios, and spaced repetition picks what comes back next. Focused treble and bass drills plus one mixed daily session are free; full access is $9.99 a month, $59.99 a year or $99.99 lifetime. There is also a free browser demo on the site.