The Livermore Time Sharing System (LTSS) was a supercomputer operating system originally developed by the Lawrence Livermore Laboratories for the Control Data Corporation 6600 and 7600 series of supercomputers.
LTSS resulted in the Cray Time Sharing System and then the Network Livermore Timesharing System (NLTSS).
References
Livermore Time Sharing System Wikipedia(Text) CC BY-SA