September October 2020 marks the 20th Anniversary of the Windows version of Minder.
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So lot’s more to come over the next 20 years.
And the name of that OS, there were a few, C/CPM , (Concurrent CPM or ), MPM, which ran on the ICL machines, and Multi-User DOS. https://en.wikipedia.org/wiki/Multiuser_DOS. We also had sites using Digital Research’s DR-Dos, which was also available as multi-user. And somebody remembers using DataPac, which later became Citrix.