There are various music apps for iOS.
But this app has a unique feature that they do not have.

Please see this app's keyboard in screenshots. Left and right are reversed!
It may be better suited to left-handed. Also, it might be a new discovery for right-handed people.
Please note that you cannot play normally.

It includes the same synthesizer engine as bs-16i (single part only). It supports all standard MIDI messages, using pre-installed GeneralUser GS SoftSynth v1.44.sf2 (S. Christian Collins), you can play various instruments.

This application supports Core MIDI output, so your play can be sent to other apps, and external MIDI hardware using Core MIDI compatible Interfaces.
Moreover, Core MIDI input also is supported, but please notice that the note number is reversed!