Windows 1.0

Windows 1.0 is (as the name suggests) the first version of Windows to be released.

People often argue whether it should be called an Operating System, or just an Operating Environment. It is 16-bit, running on top of DOS.

Development
Development of Windows started as early as 1983, when Bill Gates felt the danger of rival companies like VisiCorp, which started to make their own graphical systems to handle multi-tasking apps. At first, it was intended to be called Interface Manager, although later the name was changed to Windows. The developement had gone through a reset when the Mac was released. Before it, developers had more-or-less a free hand on how the OS will look. However, once the Mac was available, the task was made clear and simple: "Copy it!".

Trivia
Did you know... And... IT'S JUST NINETY-NINE DOLLARS!
 * It was the longest supported OS by Microsoft? It was supported for 16 years, until 2001-12-31
 * When Windows 1.0 tries to show a date later than 2000, it actually shows it as 100? Similarly, 2015 -> 115
 * This is the only OS by Microsoft to not have overlapping windows on the desktop, this was due to Apple copyrighting the overlapping windows UI