When it comes to operating systems, people usually only recall very few. If they know what an operating system is anyway. Usually it boils down to Windows, older folks might remember its roots, MS-DOS. Some might mention Linux or even UNIX. Some might heard Android is running on their smartphone or tablet. Then there is the Apple (MacOS) party. I want to talk here about OS-9, and do not refer to a version of the Apple OS by a similar name (MAC OS 9).
OS-9 was released in 1979 by Microware. It can run on Motorola 6809, Motorola 680x0 CPUs, ColdFire, SuperH, ARM/XScale, MIPS, PowerPC, Intel x86 processors. And since it is one of the first a multi-user and multitasking operating system I am intrigued. This was long before the Amiga, let alone multitasking capable Windows 95 or Linux.
While OS-9 was general-purpose computing and embedded systems, the Motorola M6809 CPU was built in the popular TRS-80 Color Computer (Coco) and similar Dragon 32/64, although not shipped with, had a potential broad user base among non business users. OS-9 was later ported for use with M68000 systems.
It is considered a "UNIX-like OS", although it is not a clone of UNIX. OS-9 is still supported by Microwave (as of 2018 when this article is written), and can run on x68 and ARM processors. But the dominance of MS-DOS and later Windows is probably the reason it never had the commercial success it deserves in my opinion.
In this video I show the (emulated) Coco running OS-9.