If you've been thinking about creating your own iOS framework, it's worth looking at the intricacies in Creating Your First iOS Framework.
Become a Swift pro with Swift Tricks Revisited.
Learn how to Create App Store Screenshots with Sketch.
Some useful projects;
Knuff: The debug application for Apple Push Notification Services
CoreDragon: Drag and drop functionality, even between applications!
FolioReader: A Swift ePub reader and parser framework for iOS.
CVCalendar: A custom visual calendar for iOS 8+ written in Swift (2.0).
Having trouble putting together an app with best practices? Check out Metronome: A Fully Unit-Tested Rx-Based Reference Application
Learn How to Make HTTP Calls on Android with Retrofit 2, the library almost everyone uses from Square.
Some projects for you to check out:
blockcanary: A transparent ui-block detection library
coolmenu: A cool cards menu concept
app-theme-engine: An easy to use app-level theme engine for Android developers
CircleLayout: An Android layout for arranging children along a circle
Tanner Christensen shares Four Things Working at Facebook Has Taught Him About Design Critique
When your app is out in the wild, you might want to do some AB testing or leak features out to small subsets of users gradually. We've been using feature toggles for a long time in our apps at Carma, and here Martin Fowler explains the concept in detail.