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.
Loads of cool apps on Sale -- June 2019
There are a lot of apps on sale at the moment. Most if not all of these are mentioned in other threads, but I thought it might be useful to put them all in one place:
Stereo Graphic EQ AUv3 Plugin
STARK Amp Simulator
K7D - Tape Delay
IMPC Pro 2
IMPC Pro 2 for iPhone
Shimmer AUv3 Audio Plugin
Auria Pro - Music Production
Audiokit: Digital D1 Synth