I've released an experimental iPad sequencer called Composer's Sketchpad: http://composerssketchpad.com
And a collaborative mini-sequencer for iMessage called MusicMessages!: http://musicmessages.io
And an Untappd-integrated app for drink tracking called Good Sprits: https://apps.apple.com/us/app/good-spirits/id1434237439
I've also dabbled in CRDT research: http://archagon.net/blog/2018/03/24/data-laced-with-history/