Windows Neptune
From BetaArchive Wiki
Windows Neptune, called Microsoft Neptune in build 5111, was planned to become the successor of the Windows 2000 family as well as the first consumer version of Windows under the NT code.
It was under development in 1999, until it was canceled, along with Odyssey to give way for Whistler, which would be named Windows XP.
Several ideas from this OS, like the login screen and user accounts panel were used in the Codename Whistler, while others such as the activity centers were eventually dropped.
