Wiktionary
n. One who shares a desk.
Wikipedia
DeskMate was a software application that provided an operating environment that competed with early versions of Microsoft Windows. It originally was made for Tandy's TRS-DOS Operating System and for their TRS-80 line of computers, but eventually shifted to PC, where it was developed using C and Assembly. Like Windows (and other competitors from the time, such as GEM), it was not a full operating system, requiring a separate disk operating system in order to function. Although the initial PC ports would only run on Tandy's PCs (such as the Tandy 1000), the introduction of the true PC-compatible computers such as the Tandy 3000 resulted in the software later being made available for other compatibles.
Some non-Tandy software used DeskMate to provide the user interface, and provided a runtime version of the operating environment for those without it. Examples included Activision's The Music Studio, and a version of Lotus 1-2-3.
Usage examples of "deskmate".
I shall have to sit all alone, for I couldn't bear to have another deskmate after you.
The next day Mirabel Cotton was kept in at recess and "gently but firmly" given to understand that when you were so unfortunate as to possess an uncle who persisted in walking about houses after he had been decently interred it was not in good taste to talk about that eccentric gentleman to your deskmate of tender years.