From the OS-9 FAQ
"OS-9 is a real-time, multiuser, multitasking operating system developed by Microware Systems Corporation. It provides synchronization and mutual exclusion primitives in the form of events, which are similar to semaphores. It also allows communication between processes in the form of named and unnamed pipes, as well as shared memory in the form of data modules.
OS-9 is modular, allowing new devices to be added to the system simply by writing new device drivers, or if a similar device already exists, by simply creating a new device descriptor. All I/O devices can be treated as files, which unifies the I/O system. In addition, the kernel and all user programs are ROMable. Thus, OS-9 can run on any 680x0 based hardware platform from simple diskless embedded control systems to large multiuser minicomputers.
Originally developed for the 6809 microprocessor, OS-9 was a joint effort between Microware and Motorola. The original version of OS-9 (OS-9 Level I) was capable of addressing 64 kilobytes of memory. OS-9 Level II took advantage of dynamic address translation hardware, and allowed a mapped address space of one megabyte on most systems, and up to two megabytes on others, most notably the Tandy Color Computer 3.
In the 1980's, Microware ported OS-9 to the 68000 family of microprocessors, creating OS-9/68000, which is used in a variety of industrial and commercial arenas, including Philips' CD-i. Code is mostly portable from OS-9/6809 to OS-9/68000 at the high-level language source code level. Code is compatible within either OS-9/6809 or OS-9/68000 at the binary level."