A monopolistic operating system that only exists in the 2010's because of the IBM-linked historical lock-in and constant useless changes of the Microsoft Word document format to prevent cross operability.
The following anecdote illustrates Windows' pervasiveness. Ciro Santilli was once tutoring a high school student in Brazil, and decided to try and get her into programming. When the "Windows is not free" subject came up, the high school student was shocked: "I paid 100 dollars for this?". She never even knew it was there. To her, it was "just a computer".
Laws should really be passed forcing OEMs to allow you to not buy Microsoft Windows when buying a computer, European Union, why have you failed me in 2016??? https://en.wikipedia.org/wiki/Bundling_of_Microsoft_Windows