There is an iOS app that is available free from Yamaha . It’s called the Yamaha Chord Tracker. The app is designed to analyze music and download it to the PSR S series keyboards but you can use the chord analysis function with out their keyboard.
It is very accurate.
It can be set to basic or advanced chords.
It shows the fingering for guitar or keyboard .
It’s works with music in the iTunes library or Drop Box

The only draw back is you get rusty when you have to do it by ear.

I hope this helps those of interest.