In 1968, when 13-year-old Bill Gates was still programming tic-tac-toe in BASIC, an engineer named Douglas Englebart at the Stanford Research Institute introduced the world to the mouse [source: Reimer]. To modern computer users, the mouse is nothing more than a mundane technological necessity: How else could you click icons, scroll through menus and move cursors? But computer users in 1968 found the mouse revolutionary precisely because no one had ever heard of those things back then.

Englebart is credited with inventing the graphical user interface, or GUI (pronounced "gooey"). In the early 1970s, a team of researchers at the Xerox Palo Alto Research Center (PARC) expanded on Englebart's concept and built the Xerox Alto, the first personal computer that featured the now-standard "W.I.M.P." GUI: windows, icons, menus and pointing device [source: Webopedia].

The Xerox Alto ran on an operating system/development environment called SmallTalk that was created in-house by Xerox PARC researchers. In 1979, 24-year-old Steve Jobs of tech upstart Apple Computer, Inc. paid $1 million in Apple stock options for a detailed tour of the Xerox PARC facility. Blown away by the SmallTalk GUI, Jobs demanded the product's technical documentation, which Xerox foolishly handed over [source: PBS].

With the specs for the SmallTalk GUI in hand, Apple released the Lisa in 1983, the first commercial computer to feature a "windows" GUI. Jobs would use a similar GUI for the much more popular Macintosh models. When Bill Gates, who wrote software for the Mac, released Windows 2.0 in 1987, Apple sued Microsoft for blatantly stealing the Mac's look and feel -- something Apple stole long ago from Xerox [source: Reimer].

Apple eventually lost the case and Microsoft's subsequent dominance of the PC market made "windows" synonymous with Windows.