Douglas Hill with everything you need to know (including all of the bugs) about presentation controllers in iOS 8+. This is going to save you hours if you haven't worked with this API before.
When considering iOS split-screen multitasking it's easy to forget some of the edge cases that your app will need to cope with. For example, what happens when the keyboard is presented from the other app when your app is in a state where you don't expect it to be shown? Keith Harrison has everything you need to know.
Fascinating story from Natansh Verma on reducing the time from a cold launch of the Facebook app to the feed being displayed. Of course, it comes down to the basics of measuring before optimising but there's a few unexpected tricks being used. There's also a good video on the same subject of Greg Moeck talking at the @Scale conference.
I linked to Roy Marmelstein's PhoneNumberKit for formatting phone number data correctly a little while ago. Looks like he's been busy recently and he's now taken on formatting for numbers, addresses and colours. There's also a write up on the library if you want more information.