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, Windows Server 2016, and Windows Server 2019
• Windows 11 and Windows Server 2022, the current version

...and most likely future versions of Windows as well.

Windows NT does not include Windows 9x/Me or Windows 3.x or older, none of which were actual operating systems, but rather graphical shells that ran on top of DOS. (Windows NT was developed from the original OS/2 codebase after Microsoft and IBM parted ways.)

ReactOS is an open-source implementation of Windows NT, specifically aimed at binary compatibility with Windows Server 2003 (NT 5.2). It is not a Microsoft product, and isn't included in any official list of Windows versions. It also isn't ready for public use, having been in alpha status for several years.

For more information, including a more inclusive list of NT versions, see Wikipedia's Windows NT entry.