GNUstep is a cross-platform, object oriented environment composed of frameworks, tools, and servers . It is very similar to the Cocoa frameworks from Apple, and tries to maintain compatibility with Cocoa wherever it is desired and possible.

GNUstep is a free software implementation of Ne XT's Open Step Objective-C libraries (called frameworks), widget toolkit, and application development tools not only for Unix-like operating systems, but also for Microsoft Windows. It is part of the GNU project.