Cocoa and Cocoa Touch:

Cocoa is a development API native to the Mac OS X operating system. Cocoa Touch is the closely-related analogous platform for the iOS. It is written in Objective-C, and acts as a sort of “top layer” to each operating system. Cocoa can be thought of as an application platform or an application development framework, but it is more integrated into the operating system than either of these would be in a Linux or Windows environment. This tight integration between the API, the operating system, and (of course) Apple’s own hardware is intended to provide a seamless development environment and enforce “the Apple way” of doing things.

Developing applications using Cocoa and Cocoa Touch involves using a set of tools developed by Apple.These development tools have a long and storied history. Originally a set of standalone application tools for the NeXTSTEP OS, they were eventually adopted by Apple for use as the official OS X tools. Later, Apple largely consolidated them into one application, known as Xcode, though some of the applications (such as Instruments and the iOS Simulator) remain somewhat separate, owing to their relatively peripheral role in the development process.