It's nice to see Apple making it even simpler to use Objective-C code in Swift. Adding these nullability flags to your source doesn't only help the interoperability between the two languages but also provides some nice compile time checks in your Objective-C code. I think this is a good sign that Apple don't see Objective-C going anywhere for a long time.
The whole issue is great (as always) but I especially enjoyed this article from Kyle Van Essen. It's basically a description of the processes they use to get their software shipped and keep quality high as they've developed Square Register from simple beginnings into a full point of sale app.
Form from Hyper provides a way to build a form on iOS using JSON and this week 1.0 was released. This project looks to be very active and they have accomplished a huge amount with it. Worth checking out if you're building any kind of data collection app.
Taylor Case gives an easy to follow article on how to prototype UIView animations with Playgrounds. This really is powerful and time saving when it comes down to the final tweaks that make a beautiful animation. In the past to get that animation exactly right took me probably hundreds of runs on the simulator.