The Tandy Color Computers included a modular ROM BASIC interpreter for the Motorola 6809 microprocessor created by Microsoft and later extended by Microware.
The Micro Computer Computer (MC-10) offers a variant of Extended Color BASIC running on the Motorola 6803 microcontroller and 4 or 16KB of RAM which enthusiasts have expanded up to 128KB with additional BASIC extensions under the name MCX BASIC.
Motorola and Microware partnered in the late 1970's to create a radically advanced BASIC for 6809-based computers, now known as BASIC09.
To support BASIC09, Microware developed an underlying operating system inspired by AT&T UNIX adapted to running on the advanced 6809 8-bit microprocessor with as little as 64KB of RAM and a single floppy diskette.
64KB machines can only run the core OS-9 known as “Level I” while machines with larger memories may run OS-9 Level II which supports the MultiVue graphical interface and much more.
Since the 1980's, OS-9 and 6809 fans have disassembled, commented, and modified OS-9 to take advantage of secret high-speed features of the Hitachi 6309 microprocessor under the project name NitrOS-9.
Some of the original NitrOS-9 fanatics also package a ready-to-run distribution of NitrOS-9 called the Ease of Use (EOU) edition.
OS-9, NitrOS-9, and Ease of Use continue to evolve and expand while providing computing experience available to home power users all the way back to 1980.
Learn more at https://microware.com/, https://github.com/nitros9project/nitros9, and http://lcurtisboyle.com/nitros9/nitros9.html
Adaptation and expansion of the UNIX: Z80 Implementation (UZI) to support a bewildering array of microprocessors and microcontrollers.
EtchedPixel's FUZIX brings a UNIX 7th edition-inspired operating system with additions and expansion galore including System III and POSIX features.
Learn more at https://fuzix.org and https://github.com/EtchedPixels/FUZIX
Mikey N6IL resurrected the 6809 version of the Flex operating system along with many additional tools.
Learn more at https://archive.org/details/color-flex-5.0.4-frank-hogg-laboratory
The widely ported and emulated CP/M operating system can run on Z80 emulation within NitrOS-9 Ease of Use Edition with several CP/M based programs available there as well.
Running Ease of Use on a CoCo3FPGA at 25MHz avoids any emulation speed penalty.
Collectors are searching for the original but rare Z80 hardware card and ROM expansion for the Color Computer.
Learn more at https://computerhistory.org/blog/early-digital-research-cpm-source-code/
Dave Dunfield's 6809 operating system for his 6809 computer build.
Learn more at http://dunfield.classiccmp.org/d6809/cubix.htm
Percom released PSYMON, the Percom SYstem MONitor, a tiny 1KB OS, for the SBC/09 single-board computer in 1979.
The source code, packed with utility routines and very well documented, was reconstructed from the original listing and ported to run on the Color Computer 1, 2, and 3 using ROM calls for the I/O.
Learn more at https://colorcomputerarchive.com/repo/Programming/Source/PSYMON%20-%20Percom%206809%20System%20Monitor/