Windows NT

Windows NT (originally standing for New Technology) was a completely rewritten variant of Microsoft Windows originally used for professional, enterprise, and server versions (while the consumer versions of Windows remained in the older implementation), but eventually became the basis for later Windows versions such as Windows XP and Windows 10. It used a new filesystem, NTFS. Although Windows versions from Windows 2000 on stopped using the "NT" name, it still shows up in how the operating system is identified internally, in places like browser user agent strings.