Have you ever stumbled across a fake "Windows 99" ISO? Or do you have a real Windows Neptune build collecting dust on a CD? Let me know in the comments—I’ll be in the virtual machine lab, trying to get Build 1515 to recognize my SATA driver.
The replies are usually a mix of sarcasm ("Just download more RAM while you're at it") and genuine confusion. But every so often, someone claims they’ve seen it. They describe a boot screen with a strange teal hue, a start menu that doesn’t quite look like Windows 98, and a build number that doesn't appear in any Microsoft archive.
But one build of Neptune leaked: . The "About Windows" dialog in this build refers to the operating system as "Windows Neptune (Beta)" with a build date of December 1999. If you squint, that is technically a Windows operating system from 1999. However, it is not called "99," and it runs the NT kernel—meaning many DOS games would not work on it.
Development was canceled in early 2000, and its features were merged into what became Windows XP.