A Data General operating system developed in the 1970s or 1980s. When used in conjuction with a BASIC (e.g. Business Basic) it could support 16 concurrent users at the record locking level and two printers all on 128K memory.
Reputedly IBM wanted to license this for the first IBM PC but DG turned them down so they went to Microsoft instead. How different the world could have been.
[Before or after IBM wanted CP/M?]