Windows Neptune

Neptune

A version of the Microsoft Windows operating system
Neptune build 5111 logon screen
Developer	Microsoft
Working state	Historic, never released
Latest preview	5.50.5111 / December 27, 1999; 17 years ago (1999-12-27)
Kernel type	Windows NT
License	Non-disclosure agreement
Official website	windows.microsoft.com
Support status
Never released

Neptune was the codename for a version of Microsoft Windows under development in 1999. Based on Windows 2000, it was to replace the Windows 9x series and was scheduled to be the first consumer version of Windows built on Windows NT code.

Neptune largely resembled Windows 2000, but some of the new features introduced, such as the firewall, were later integrated into Windows XP as the Windows Firewall. Neptune introduced a logon screen similar to that later used in Windows XP. Neptune also experimented with a new HTML and Win32-based user interface originally intended for Windows ME, called Activity Centers, for task-centered operations.

Only one alpha build of Neptune, 5111, was released to testers under a non-disclosure agreement, and later made its way to various beta collectors' sites and virtual museums. Build 5111 included Activity Centers, which could be installed by copying ACCORE.DLL from the installation disk to the hard drive and then running regsvr32 on ACCORE.DLL. The centers contained traces of Windows ME, then codenamed-Millennium, but were broken due to JavaScript errors, missing links and executables to the Game, Photo, and Music Centers. In response, some Windows enthusiasts have spent years fixing Activity Centers in build 5111 close to what Microsoft intended.

In early 2000, Microsoft merged the team working on Neptune with that developing Windows Odyssey, the upgrade to Windows 2000 for business customers. The combined team worked on a new project codenamed Whistler, which was released at the end of 2001 as Windows XP. In the meantime, Microsoft released another home user 9x-based operating system called Windows Me.