What is Longhorn Linux?
Longhorn Linux was a Ubuntu transformation pack designed to make the Ubuntu desktop look like the desktop of the cancelled Windows OS, Longhorn. The project was entirely open source and developed by a team of volunteers.
The project was started on the 2nd of November 2009 on Joejoe.org, a popular Desktop modification site during the early 2010s, by jman6495.
Longhorn Linux was originally a Linux distribution based on Ubuntu, that was downgraded to a Desktop Transformation Pack by popular demand from the Ubuntu community.
The final release was Longhorn Linux Pack 6000 Alpha, which you can download here.