Microsoft finally open sources DOS 1.0 - and it's so much more than the code

Microsoft finally open sources DOS 1.0 - and it's so much more than the code ...

Before Mac OS X, There Was OS 1 Through 9: A History of Apple's Operating System

A retrospective on Mac OS from I to X showcases Apple's evolution in operating systems over the years.
Ars Technica

Though “barely an operating system,” DOS still matters (to some people)

Earlier this month, I spent a day working in the throwback world of DOS. More specifically, it was FreeDOS version 1.1, the open source version of the long-defunct Microsoft MS-DOS operating system.