Ah, RSTS. RSTS was an OS (of sorts) for the DEC PDP/VAX series of minicomputers. The name is an acronym meaning Resource Sharing/Time Sharing. It was best used on VT100 or VT52 terminals connected by serial muxes to the host computer, although it drove many a DECWriter in its time. Rights for RSTS are presently held by a company named Mentec, Inc. which allows its distribution to PDP-11 enthusiasts for use on the machines themselves or on modern emulators which run on Windows, Linux, etc.