NexusOS

 (formerly SimpleOS) is an operating system developed by Tesseract Labs. It was first released in 2003.

History
NexusOS was forked from a different operating system called SimpleOS, after Tesseract Labs acquired the OS and shut down development. It was first released on March 2003. At first nexusOS was just a version of SimpleOS with a different GUI and some additional features and apps. Over time nexusOS kept getting more different than SimpleOS, including completely rewriting the kernel in version 3.0 (released in 2008) and switching the codebase to a more stabler one. The latest stable release is nexusOS 7 in 2019.