This is where it all started for Windows. The original Windows 1 was released in November 1985 and was Microsoft’s first true attempt at a graphical user interface in 16-bit.
Development was spearheaded by Microsoft founder Bill Gates and ran on top of MS-DOS, which relied on command-line input.
It was notable because it relied heavily on use of a mouse before the mouse was a common computer input device. To help users become familiar with this odd input system, Microsoft included a game, Reversi (visible in the screenshot) that relied on mouse control, not the keyboard, to get people used to moving the mouse around and clicking onscreen elements.