Sigma OS

Sigma OS
Crusty Windows bootleg
The desktop of Sigma OS
The desktop of Sigma OS
Original OSWindows Longhorn Build 4074
Release dateMarch 8, 2013
Architecture(s)x86 (32-bit)
File size1.1 GB
Download linkSigma OS 3.0 M6.iso
Date addedDecember 27, 2021
Live CDNo

Sigma OS is a series of mods based on Windows Longhorn designed to make it more stable and "usable". It was created by techvortal. The latest version, M6, which is based on Longhorn build 4074, was released on March 8, 2013. It was added to the archive on December 27, 2021.


The bootleg itself is based on Longhorn build 4074, which was a Milestone 7 build of Windows Vista, which released in April 2004, before the development reset. The OS is mostly stock except for some integrations, icon replacements, and themes. Certain programs are taken from other Longhorn builds in order to make it more "stable".

Changes from Longhorn 4074

  • The default theme has been replaced with a theme called "Aero mod" by urban92.
  • Some Longhorn updates have been added.
  • The cursor has been replaced with the one from Windows Vista build 5384.4.
  • The sounds have similarly been replaced with the ones from Windows Vista build 5384.4.
  • Some icons have been replaced with ones from Windows Vista.
  • The 180 day timebomb from the original build has been removed, so you do not need to change the date to use this mod.


  • 7-Zip 9.20
  • Paint.NET v3.36
  • Opera 12.14


  • Windows Update is not present.