Cocoa in a Nutshell

Chapter 3. The Application Kit

The bulk of the Application Kit (or AppKit) is comprised of classes for user interface components, from windows and widgets to colors and fonts. From the perspective of an application, the central class is NSApplication , which manages much of the basic application architecture, from loading user interface definitions to setting up the run loop to handle events, which relieves you of much of the nitty-gritty often associated with simply making an application tick. The AppKit also provides many architecture-related classes for document management, printing, and interaction with the workspace.