OpenStep
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NeXTSTEP's programming interface pried loose from its operating system, specified by NeXT and Sun in 1994 and later the foundation of Cocoa.
NeXT sold too few computers, but plenty of people wanted its software. OpenStep was NeXT and Sun's attempt to turn the object-oriented Objective-C frameworks of NeXTSTEP into an open standard that could run on top of other systems. NeXT shipped OPENSTEP for its own Mach kernel and for Windows NT, and Sun released a version for Solaris.
Sun lost interest once Java arrived and backed CDE as its Unix desktop, so the standard never got the many implementations its name promised. It got an owner instead: Apple bought NeXT in 1996, and the OpenStep API became Cocoa in Mac OS X. The NS class prefix in every macOS app is what's left. The free reimplementation GNUstep lives on, not least behind Window Maker.