DESQview was developed by Quarterdeck Office Systems which released it in July 1985, four months before Microsoft introduced the first version of Windows. At the time, DESQview was the first program to bring multitasking and windowing capabilities to a DOS environment in which any exisisting DOS programs could be used.
Under DESQview, DOS programs could be run concurrently in resizable, overlapping windows (something the first version of Windows could not do). A simple hidable menu allowed cutting and pasting between programs. DESQview allowed simple editable macros as well. Quarterdeck also developed a set of optional utilties for DESQview including a notepad and dialer. Later versions allowed graphics mode programs to be loaded as well, but only run in full screen mode.
DESQView was not a full-fledged GUI operating system; it was a quasi-GUI shell that ran in real mode on top of DOS. Although it could be configured to run on an Intel 80286-based PC AT with two megabytes of memory, it really came into its own on Intel 80386 machines which were better at utilizing memory above DOS's limit of 640kb. However, in either case, it ran in real mode rather than protected mode, meaning that a misbehaving program could still crash the system.
DESQview was critically acclaimed and won many fans, but it never met with mass appeal, despite Quarterdeck's sustained efforts to win people over. Reportedly it intrigued many people at Microsoft, including Bill Gates, who by some accounts based his first version of Windows on DESQview and two other early GUIs, VisiOn and GEM. In one arena, however, DESQview was a lasting success: many multiuser bulletin board systems were based on it, thanks to its modest hardware requirements, its robust multitasking. and superlative handling of multiple communication ports.
To make maximum use of extended memory (between 640kb and 1Mb) in conjunction with expanded memory (above 1Mb) for DESQview, Quarterdeck developed a sophisticated memory manager. Owing to the foresight of its marketing manager, Quarterdeck marketed it as a separate product, QEMM (Quardeck Extended Memory Manager). It became more popular than DESQview itself, and sold steadily for many years, generating over $150 million in sales from 1987 through 1994. Eventually it was "killed" by the 3.1 version of Windows because Microsoft chose to make the latter incompatible with QEMM.
In the mid 1990s, Quarterdeck tried to recast itself as an Internet company without having any Internet products. For a time, rumor circulated of an X-windows version of DESQview, but it never appeared. Eventually, the company was acquired by Symantec.