The purpose of this project is to create a free and open version of
the Cocoa (formerly known as NeXTSTEP/OpenStep) APIs and tools for as
many platforms as possible.
GNUstep provides a robust implementation of the AppKit and Foundation
libraries as well as the development tools available on Cocoa,
including Gorm (the InterfaceBuilder) and ProjectCenter
(ProjectBuilder/Xcode). GNUstep currently supports Unix (GNU/Linux and
GNU/HURD, Solaris, NetBSD, OpenBSD, FreeBSD, Darwin) and Windows.
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GNUstep provides an environment to easily develop applications. GNUstep is suited both for advanced GUI desktop applications as well as for server applications. GNUstep provides the foundations for a portable desktop environment, but delegates this task to other projects.
GNUstep seeks to be source code compatible with Cocoa, it can thus
be used to develop and build cross-platform applications between
Macintosh (Cocoa), Unix and Windows.
GNUstep's main development language is Objective-C, but GNUstep is not
limited to that.
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Hacker Threads offers GNUstep shirts here. All profit from the shirts benefit the project.