AmigaOS. Mostly because of the underlying hardware and ecosystem. Simple things were simple, and complex things were complicated but possible. Today everything

AmigaOS. Mostly because of the underlying hardware and ecosystem. Simple things were simple, and complex things were complicated but possible. Today everything is complex and complicated for little reason. (Compare e.g. the elegance of Amiga Message and signal ports to named pipes / shared memory / tcp / whatever. Of course it can be emulated - but the fact it’s standard on the Amiga means every program uses it and it makes a huge difference in interoperability. Similarly, IFF was good enough; there weren’t billions of framing formats on the Amiga, because there was an acceptable standard from day 1)