Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
Media Assistant and Onemotion music web apps
There are a couple of very nice, free, web based music apps that I've been using for a few years from developer Tomas Eriksson (onemotion.com). You can actually use a MIDI controller with them if you use a supported browser (such as Chrome) on a PC. It's pretty convenient because you can create, save, export your own projects and then access them on any browser.
Using the Media Assistant app on iOS enables them to be used in AUM where audio can be recorded live and effects added. There are some limitations using it this way, one of them being that Media Assistant must be in the foreground in AUM to play, and there's no way to sync the transport with the web app, but I still find it fun to experiment with.
Here's a short video of one of them in action:
Media Assistant and Onemotion app in AUM
There are two web based apps:
They are both quite sophisticated and offer a lot of features and control, and totally free, and the developer has improved them quite a bit over the last couple years. There's also a Facebook group out there for it too. I'm not going to go into the details on how they work here, but feel free to hit me up if you have questions, and I'll try to answer.