Windows Neptune

Windows Neptune
Version of the Windows NT operating system
Neptune build 5111's desktop
DeveloperMicrosoft
Working stateHistoric, never released
Latest preview5.00.5111 (kernel reports)
5.50.5111 (version in many files) / December 27, 1999 (1999-12-27)
Marketing targetConsumer
Kernel typeHybrid (NT)
LicenseNon-disclosure agreement
Support status
Cancelled

Neptune was the codename for a version of Microsoft Windows under development in 1999. Based on Windows 2000, it was originally intended to replace the Windows 9x series and was scheduled to be the first home consumer-oriented version of Windows built on Windows NT code. Internally, the project's name was capitalized as NepTune.