I'm really impressed by the Chordie App that takes a MIDI signal from a keyboard and in real-time displays the notes played via:
in chord notation (e.g. A minor 7).
This is incredibly useful for those online music teachers who need to explain harmony to a wide variety of people.
The app has been developed by a music software developer working on their own.
They are about to release a new version of the software and have released a video explaining the new features.