The 1984 Macintosh did not invent the graphical user interface, but it packaged mouse-driven windows, icons, menus, and direct manipulation into a mass-market personal computer with unusually consistent application behavior.
The X Window System separated graphical applications from the display server through a network protocol, giving Unix workstations a portable windowing foundation that could span vendors and machines.
Susan Kare transformed tiny monochrome pixels into icons and typefaces that made the original Macintosh feel expressive, legible and approachable, helping define the visual vocabulary of graphical personal computing.
Ben Shneiderman's theory of direct manipulation explained why visible objects, incremental actions and rapid reversible feedback made graphical interfaces feel easier to learn and control.
The Xerox Alto combined a bitmap display, mouse, Ethernet and interactive software into a personal networked workstation that became a laboratory for modern graphical computing.
Xerox Star transformed PARC research into a commercial office system whose icons, folders, document-centered desktop and consistent generic commands were designed through an unusually systematic HCI process.
Apple Lisa brought a mouse-driven graphical desktop into the personal-computer market while its designers repeatedly tested and revised icons, documents, menus and desktop behavior.
The original Macintosh made windows, icons, menus, the Finder, QuickDraw and direct-manipulation interaction part of a coherent mass-market operating environment.