Want to try it out?

    wget -O a.img https://github.com/roelandjansen/pcmos386v501/blob/master/IMAGES/PCMOS386-9-user.img?raw=true
    qemu-system-i386 -fda a.img

I can almost get serial working:

    printf 'memdev = $386.sys /p\r\n' > config.sys
    printf 'device = pcterm.sys\r\n' >> config.sys
    printf 'device = $serial.sys /ad=03f8,in=4,hs=x,ib=2048,ob=2048\r\n' >> config.sys
    printf 'smpsize = 80k\r\n' >> config.sys
    printf 'buffers = 40\r\n' >> config.sys
    touch -mt 9311171533 config.sys
    mcopy -n -o -i a.img -m config.sys ::

    printf 'addtask 300k,1,,user01,pcterm,1,19200\r\n' > autoexec.bat
    touch -mt 9311171533 autoexec.bat
    mcopy -n -o -i a.img -m autoexec.bat ::

    qemu-system-i386 -fda a.img -chardev socket,server,host=127.0.0.1,port=4555,id=com1 -serial chardev:com1 -rtc base=1994-06-17T16:01:21

(then in another window)

    nc localhost 4555

Perhaps a better link is the github repository? https://github.com/roelandjansen/pcmos386v501 That has a decent README and a link to Wikipedia which is quite comprehensive (I'd never heard of this OS before ...)

Maybe but the OP link has links to both of those and summarizes quite neatly what this is IMO.

I actually used this OS in 1991 (with an X.25 card) to make a 12 station (over two sites) POS system. That main station was a 486 and all the terminals were 286s.

It worked very, very well.

   8
   Insufficient disk space to install Operating System.
   PC-MOS Requires 800k to store systems files.
   Press F10 to Exit to PC-MOS.
   [PCMOS]

https://github.com/roelandjansen/pcmos386v501/blob/master/SO...

No Borland compiler suite yet, which hurts, but I understand the enormous difficulties of getting that sort of thing into public hands.

I need to dig through my old software to see if I still have some of the software from back then. I think I still have a MS-DOS BASIC (WBASIC?) disc or two. The MS-DOS compatibility was one of the great things about PC-MOS.

Search for "abandonware". I personally like this[1] project; it isn't in English but their archive is really good, and Google Translate works.

[1] http://old-dos.ru/index.php?page=files&mode=files

A multi-user, multi-tasking MS compatible DOS?

There was another such system back in the day called TSX-32. Before I had discovered Linux and heard of TSX-32, my dream as a kid was to create a multi-user DOS.

[I'd paste the link but the Android paste popup isn't opening for some reason.]

Digital Research also produced Concurrent DOS (later renamed to Multiuser DOS), which I think was based on Concurrent CP/M-86.

I would love to see something like this running -natively- on an ARM processor especially on the Raspberry Pi.

Seems it has its own filesystem, maybe somebody will shove this into a FUSE module. :- )