MusicMessages! is a collaborative step sequencer for the iMessage App Store (iPhone, iPad). Using the simple and (hopefully) intuitive interface, you can punch in a few chords or a percussion line and send the message off to your friends, who can then make their own changes and send it back. Five instrument layers and over 40 MIDI instruments are available to use. Bonus: if you have an iPhone 7, the note buttons respond to pressure and "pop" like bubble wrap with the help of the Taptic engine!
Composer's Sketchpad is an iPad sequencer-ish app for quickly jotting down musical ideas. In brief, the app presents you with a giant pannable and zoomable canvas that you can draw musical notes on. I wanted to create a modern take on sheet music, but without any of the legacy limitations; as a result, you can start each note at any time and bend it to any pitch, giving you the ability sketch out expressive solos and complex rhythms with no extra effort. (You can also turn on time or pitch snapping if you like.) Navigation, editing, and playback are carefully designed to be as frictionless as possible, and over 100 different instruments (as well as a percussion set) are available. Your music is saved automatically without any limit on the total number of sketches. Apple Pencil supported! [more inside]