I used to be a systems integrator for the TRS-80 Model 16's. we would hack them to add extra serial cards to get 8 serial ports! You could have 9 people logged in at once and doing well if the application was carefully designed.

Funny but true it ran Microsoft Xenix!! http://en.wikipedia.org/wiki/Xenix and had a Microsoft Multiplan (excel like) you could run from a tty or the console.

I have a customer who still has a running copy of Microsoft Multiplan that I have to hack once in a while to keep runnning. It's quite amazing that this customer still keeps a ton of stuff in that old system using telnet/ssh to the SCO Unix box that they host Excel on.

I did my first commercial C code development on these monsters! After a time I even had one in my house so I could do development at home without 1200baud modems dropping my connection etc. And I had a "test" environment to develop code before deploying to my customers machines.

I had all my customers setup with UUCP so they could email me and my staff and alerts from low disk space, backs etc would come to us at the central machine via UUCP emails.

Those were the days.. ;-)

EDIT: iPad autocorrect pain and corrected memory error