iOS

iOS is the world’s most advanced mobile operating system, continually redefining what people can do with a mobile device. Together, the iOS SDK and Xcode IDE make it easy for developers to create revolutionary mobile apps.
Site: https://developer.apple.com/technologies/ios

Books

Added Swift Essentials - DZone Refcard

Get ahead of the fastest growing programming language. Swift is an open source, type-safe, object-oriented programming language that is used for more than client-side mobile apps. It is designed for developers to have an easier time writing and maintaining accurate code.

 Free book

Added Mastering iOS Game Development

iOS is an operating system for Apple manufactured phones and tablets. Mobile gaming is one of the fastest-growing industries, and compatibility with iOS is now becoming the norm for game developers. SpriteKit is part of the native SDK from Apple, and enables developers to make simple entry into game development without unnecessary overhead and a long learning process.

 Free book

Added iOS Succinctly

The companion to Objective-C Succinctly, and your practical introduction to developing for iOS.

 Free book

Added iOS 8 Day by Day

A review of all the important part of iOS 8 for developers. Presented in 39 easy to digest chunks, each with a sample project.

 Free book

Added Swift Cheat Sheet

A short guide to using Apple's new programming language, Swift.

 Free book