A thesis by Jian – Xiong Shao, 1983, titled OUP/M – A 6502 Operating system, contains a floppy disk based operating system for the 6502. It is modelled after CP/M and follows the same design principles.
In the development of OUP/M, an OSI C-3 microcomputer system was used. This system consists of a 6502 CPU, a dual 8-inch floppy disk drive, a console, a printer, and 56 K bytes of RAM.
On this machine all I/O is memory mapped and address space layout has to be taken into consideration.
For years only the document was available, archived on archive.org, with the source in the document.
Jian – Xiong Shao did not publish more 6502 code, further implementations are unknown.