[snip] Roy, The NorthStar Horizon ran TurboDOS and there were special versions of the Horizon specifically to run multiuser applications. The manuals are available here: http://www.hartetechnologies.com/manuals/Northstar/ I think Dave Dunfield has some TurboDOS disk images on his site: http://www.classiccmp.org/dunfield/img/index.htm I suppose in theory you could boot his Horizon simulator with the TurboDOS images and use the manuals to experiment with it. If you really want to use real hardware, you could either buy one of the specially modified Horizons or just upgrade a normal one. I have seen the Horizon multi serial port and the "slave processor" cards on Ebay from time to time. Thanks and I wish you the best of luck with your search. I hope this helps. Andrew Lynch