NeXTSTEP

NeXTSTEP was the Unix-based operating system developed by NeXT, the company founded by Steve Jobs after his departure from Apple in 1985. Built on a Mach kernel and a BSD userland, NeXTSTEP distinguished itself not through its kernel innovations but through its object-oriented programming frameworks — the Foundation and AppKit libraries written in Objective-C — and its development tools, including Interface Builder. These frameworks, which embodied the dynamic dispatch and message passing semantics of the Objective-C runtime, became the direct architectural ancestor of Apple's Cocoa and iOS frameworks.

When Apple acquired NeXT in 1997, it acquired an operating system that had already failed as a commercial product but had succeeded as a software architecture. NeXTSTEP's lesson is that the systems that outlast their business models are those whose runtime architectures enable frameworks to evolve faster than the languages they are written in. This is not a historical curiosity; it is a design principle that every modern platform architect ignores at their peril.