OpenStep

OpenStep is an Application Programming Interface (API) for creating applications using the Objective-C language. It was published by NeXT Computer Inc. in 1994.

OpenStep consists of three parts:

• the FoundationKit, a library of non-graphical objects;
• the AppKit, a library of objects useful in creating graphical applications;
• and Display Postscript, an interface for drawing to the screen using the PostScript graphics language.

The OpenStep specification is available in a couple of different formats from [1].

Commercial successor of the OpenStep is Apple's Cocoa.