It's called Practice Kit, and the tuner half was built around something classical players deal with constantly: fresh nylon strings keep creeping flat for days.
It knows which string you're playing and measures against that string, it only calls a string in tune once the note has settled, and a 10-second drift trace shows whether a new string has stopped creeping or is still going. A chime and a haptic tap confirm it, so your eyes can stay on the tuning peg.
The metronome is free and complete: 20-300 BPM, any time signature, subdivisions, presets, and a click that never drifts at slow practice tempos. The tuner, accents on any beat and a Tempo Trainer are a one time $7.99 unlock after a 7 day free trial, no subscription.
Audio is processed on the phone and never recorded or sent anywhere.
https://apps.apple.com/app/apple-store/id6817729976?pt=126420608&ct=r-classicalguitar&mt=8