Windows Odyssey

Windows Odyssey is a codename for a cancelled version of the Microsoft Windows operating system intended to succeed Windows 2000. It was later combined with Windows Neptune to create Windows XP.

Development
Windows Odyssey was intended to replace the business-oriented Windows 2000. Development began in the 1990s and was based on Windows 2000. The version number of Windows Odyssey is still unknown and unverified sources claim it as Windows NT "5.5" or "6.0". Features found in Windows Odyssey was the new Activity Center and the new user interface. However, due to high hardware requirements and because Windows Odyssey and the consumer-based Windows Neptune were based on the same codebase, Microsoft combined them to form codename "Whistler" which would later be Windows XP for efficiency. No version of Windows Odyssey was officially released.

Confidential documents from the Comes vs. Microsoft case do state that Windows Odyssey was indeed under development.