An interesting operating system with file system compatibility to CP/M-80 (and other similarities).

"What I (Richard A. Leary) have done is attack the software side of the problem in order to make any 6502 system a truly workable disk based system. In addition a degree of compatibility is now possible not only between 6502 systems but with large parts of the world of CP/M systems. The result of my efforts is a system of software which I have named DOS/65."