DESQview
DESQview was released in July 1985, four months before Microsoft introduced the first version of Windows. It was widely thought to be the first program to bring multitasking and windowing capabilities to DOS, but in fact there was a predecessor, IBM's TopView, released in 1984, from which DESQview inherited the popup menu.
Under DESQview, well-behaved 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 provided support for simple editable macros as well. Quarterdeck also developed a set of optional utilities 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 run on any Intel 8086- or Intel 80286-based PC. It could also use expanded memory add-ons to workaround the 640kb RAM limit of Conventional memory on early PCs. DESQview really came into its own on Intel 80386 machines which were better at utilizing memory above DOS's limit. However, in either case, it ran in real mode rather than protected mode, meaning that a misbehaving program could still crash the system.
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