This is the source for the Concurrency app: https://itunes.apple.com/app/concurrency/id738872892 - enjoy!
Just so we're clear, I'm releasing this so you can study it and learn how to make apps (or how not to make them, depending on what you think of my code).
This is not an invitation to take my app and release it unmodified (or mostly unmodified) under your own name. If you do that, I will find you ಠ_ಠ.
If you like this, please buy my app! KTHANXBAI