Nomad AI OU released Chord AI, which claims to use Artificial Intelligence to detect chords in music. There is no evidence to support this claim on the developer's YouTube channel, where he is just showing off other apps.
The app is free to try though, and $4 to Unlock via IAP. [Updated. Thanks to SodaMountain for pointing out the IAP price increase from $1.]
Chord AI App Store Description:Chord AI uses recent advances in AI to give you the chords of any song automatically. You won't need anymore to look for the chords of a song on the web.
Chord AI works offline. You don't need to have an internet connection unless you want to play a song from YouTube or a streaming service.
Chord AI currently recognizes all major and minor chords. Recognition of rare chords such as seventh, ninth, augmented, diminished chords etc. will be available in later updates. Please be patient :)
Chord AI can find the chords of a song in two ways:
1) Through your device microphone. Any song playing around you, or played by your device, and the chords of the song are shown in real time.
2) For audio files that you have on your device or iCloud, Chord AI will process the file in a few seconds to give you all the chords of the song at once
Any feedback appreciated at email@example.com