Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
iOS Design Kit - The newest library of native iOS templates
Sketch - Professional digital design for Mac.
iOS Design Course - The Complete iOS Design Course with Sketch from Bitfountain
Invision - Prototyping and collaboration for design teams
Xcode - Xcode is Apple’s powerful integrated development environment for creating great apps for Mac, iPhone, and iPad. Xcode 4 includes the Xcode IDE, instruments, iOS Simulator, and the latest Mac OS X and iOS SDKs.