Back in 2014, Microsoft launched the Windows Technical preview program for Windows 10. Later, it was officially named as “Windows Insider Program” and has helped Microsoft test and get feedback on the OS before it’s released to the public.
While the program is still new, it looks like Microsoft had a vision for it almost 20 years ago. Back when Windows 95/98 were popular, Microsoft was working on Windows Neptune. According to a recent tweet by Albacore, Microsoft had an almost working Insider program and from the looks of it, was actively using it to test Windows updates. Back in 1999, Microsoft was using self-hosting mechanism to seed the new updates to testers without having to format the system using ISO files.
Old betas, especially of projects Microsoft was very passionate about, never cease to disappoint. Here's a selfhosting mechanism in 1999's Codename Neptune. The idea that something like today's Insider program (in terms of ease of use) already existed back then is wild. pic.twitter.com/tM4IJASCE0
— Albacore (@thebookisclosed) January 5, 2020
You can read more about Project Neptune here. Microsoft used to release Developer and Consumer previews of their OSes back in the day but those were almost finished versions with few bugs. Windows Neptune, unfortunately, never saw the light of day but it helped Microsoft develop the Windows Update system that has been used in the modern Windows Operating System.