Something for the mobile studio. It does audio and midi. It's not free but the cost is nil.
 
https://play.google.com/store/apps/details?id=com.extreamsd.aemobile
 
Go HERE for the save-disabled demo.
 
"The most powerful multi track audio and MIDI recording studio on Android with support for over 250 USB audio and MIDI interfaces (*), virtual instruments(*), editing with unlimited undo/redo, mixing, real-time effects, automation and much more! Record your voice, guitar, piano or any other audio source or create beats and synth tracks using a piano roll or external MIDI keyboard."
 
 
 
Oh, and when you're at home you can mirror it on your computer full screen and use mouse and keyboard with Mobizen.

I have this, as well as the licenses for their custom Android USB audio driver and their MIDI driver. It requires a core-compliant audio i/f. Works great with my otherwise unusable PreSonus AudioBox 44VSL. I was really happy with it...until last week. That's when I was trying to set up a project template to use for recording a 13-member a cappella group using an M/S mic pair.
 
Crash and burn.
 
Not possible to set up a monitoring mix. Why not? It never occurred to me to check for a feature that to me seems so basic as to be ubiquitous. The feature?
 
Phase inversion.
 
No can do.
 
I haven't had time to contact the vendor yet, so it's possible that phase inversion will be added at some point, but not now.
 
I have found no way with AE Mobile to decode the mid and side audio tracks to stereo L/R.
 
Whether or not you need phase inversion, it's still the only viable solution on Android. It gets supported and it gets updated.
 
I have about US$20 invested in the 3 licenses (AE Mobile, USB driver, MIDI driver). I've spent more on a single bad opportunity in a bar.

soens
Oh, and when you're at home you can mirror it on your computer full screen and use mouse and keyboard with Mobizen.

That's something I'm definitely going to have to check out!
 

I will give AE huge kudos for what its capable of ....as It was my main way for recording for a few years before i dove into the laptop/cakewalk recording mode.  That app is awesome for on the fly and i was always amazed at the quality recording I would get via the galaxy s3/4 phones I had the app on.   I never got to the midi stage with it.   Its a great mobile tool for recording guitar/drums/vox ideas on the fly if traveling. 

Well, guess what? There IS phase inversion. It's an effect that you add as an Insert. I emailed them last night, got the answer about 7 this morning, replied with a "thank you" and a note that my last name is German and not Dutch (I'm nothing but a simple 'but' in Dutch ), and got a reply back immediately.
 
GREAT customer service from eXtream Software Development!

They were always very quick to respond to emails...and many cool effects built into the app...for a phone recorder...none better..