I fondly remember Apple's Human Interface Guidelines for the Macintosh, and software that followed it. Even if you'd never seen a given application before you c

I fondly remember Apple's Human Interface Guidelines for the Macintosh, and software that followed it. Even if you'd never seen a given application before you could easily discover its features and how to operate it. Having said that, I think CLI programs tend to not get enough credit for discoverability. It's just a different kind of discoverability (man $program, $program --help).