Quickly: Gates's monopolistic business practices created a significant benefit for technology users -- a set of standards that greatly streamlined communications and work.
I've grown up with and lived with Bill Gates as the most influential technology leader of the era. Even though he has been slowly backing out of Microsoft for the last five years, his actual July 1, 2008 departure from the company is a milestone worth reflecting on.
What is his single most important legacy? The ability, through monopolistic business practices, to make Microsoft's products global, de facto standards for business and consumers. This created a standard ecosystem of documents, spreadsheets, printer drivers, programs, browsers, and operating systems which enabled people to communicate in a single "language" -- greatly easing the inherent limitations of computer systems.