Microsoft (Fictionalized)

Pre-9x

 * Windows 1.0 (1985)
 * Windows 2.0 (1987)
 * Windows 3.0 (1990)
 * Windows 3.1 (1992)
 * Windows for Workgroups 3.11 (1993)
 * Windows 4.0 (1994)

9x

 * Windows 95 (4.1) (1995)
 * Windows 96 (4.2) (1996)
 * Windows 97 (4.3) (1997)
 * Windows 98 (4.5) (1998)
 * Windows 99 (4.51) (1999)
 * Windows ME (4.9) (2000)

NT

 * Windows NT 3.1 (1993)
 * Windows NT 3.5 (1994)
 * Windows NT 3.51 (1995)
 * Windows NT 4.0 (1996)
 * Windows NT 5.0 (1998)
 * Windows 2000 (NT 5.1) (1999)
 * Windows 2001 (NT 5.2) (2000)

Modern

 * Windows XP (NT 5.5) (2001)
 * Windows XP Second Edition (AKA Windows XPSE) (NT 5.51) (2002)
 * Windows Longhorn (NT 6.0) (2004)
 * Windows Vista (NT 6.1) (2007)
 * Windows 7 (NT 7.0) (2009)
 * Windows 7.1 (NT 7.1) (2010)
 * Windows 8 (NT 8.0) (2012)
 * Windows 8.1 (NT 8.1) (2013)
 * Windows 9 (NT 9.0) (2014)
 * Windows 10 (NT 10.0) (2015)
 * Windows 11 (NT 11.0) (2018)
 * Windows 12 (NT 12.0) (2020)

Server
(Previous server OSes were part of the NT family.) (Starting with Windows 9, server releases are part of the main Windows line.)
 * Windows XP Server Family (2001)
 * Windows Server 2003 (based on XPSE) (2003)
 * Windows Server 2005 (based on Longhorn) (2005)
 * Windows Server 2008 (based on Vista) (2008)
 * Windows Server 2008 R2 (based on Win7) (2009)
 * Windows Server 2012 (based on Win8) (2012)
 * Windows Server 2012 R2 (based on Win8.1) (2013)