A free app for Android, by Boundary Effect.

Want to play your Midi keyboard and record the music you will make on your Android device? The Midi Host can help you do just that. This convenient app allows you to connect your Midi keyboard without a hitch, since you don’t have to configure or set anything else. Just plug your instrument and you are ready to go.

In this app, you can enable the OTG mode to connect the Midi keyboard. It also allows you to control the volume so you can comfortably hear the music you will make. Another convenient thing about this application is that it supports legacy devices that the Marshmallow Midi API doesn’t.