Ben Scheirman on designing a robust download system taken from his experiences building the NSScreencast app. He covers persisting the download, pausing and resuming,
handling failures and dealing with downloads without Wi-Fi. He then wrote an additional article all about background downloads too.
Brandon Alexander with a three part (1, 2, 3) article on all of the different types of interaction events in iOS. If you've ever had a question about whats going on with touch handling, the responder chain, or even just target/action. This is a clear and simple explanation of them all.
This library from Toto Tvalavadze is kinda interesting. Everything included here is possible by simply listening for the notifications, but I liked the encapsulation of it and how it copes with edge cases like keyboards which show from other apps while running alongside yours.
Just a quick one to finish, if you're using Core Data and mogenerator, there's a new version out which supports Swift 3. If you're using Core Data without mogenerator, you should certainly give it a look.