Windows NT
Windows NT is the current line of Windows operating systems developed by Microsoft. This includes:
- Windows NT 3.1 through 4.0
- Windows 2000 (NT 5.0)
- Windows XP (NT 5.1) and Windows Server 2003 (NT 5.2)
- Windows Vista and Windows Server 2008 (NT 6.0)
- Windows 7 and Windows Server 2008 R2 (NT 6.1)
- Windows 8 and Windows Server 2012 (NT 6.2)
- Windows 8.1 and Windows Server 2012 R2 (NT 6.3)
- Windows 10 and Windows Server 2016 (the current version)
...and most likely future versions of Windows as well.
Windows NT does not include Windows 3.x or Windows 9x/Me, none of which were actual operating systems, but rather graphical shells that ran on top of DOS. (Windows NT was developed from the OS/2 codebase.)
For more information, including a more inclusive list of NT versions, see Wikipedia's Windows NT entry.