GNUstep is a free software implementation of the Cocoa (formerly OpenStep) Objective-C frameworks, widget toolkit, and application development tools for Unix-like operating systems and Microsoft Windows.

Apart from the default Objective-C interface, GNUstep also has bindings for Java, Ruby,[1] GNU Guile and Scheme.

GNUstep thus predates Cocoa, which emerged when Apple acquired NeXT's technology and incorporated it into the development of the original Mac OS X, while GNUstep was initially an effort by GNU developers to replicate the technically ambitious NeXTSTEP's programmer-friendly features.

GNUstep began when Paul Kunz and others at Stanford Linear Accelerator Center wanted to port HippoDraw from NeXTSTEP to another platform.

GNUstep contains a set of graphical control elements written in the Objective-C programming language.