A Honeywell operating system promised as a sop to customers after canning Multics in 1985. Opus was to provide everything Multics had and more, plus total compatibility with the Level 6/DPS6 operating system.
"Opus" was a code name, the system was officially named VS3 (short for HVS R3 or Honeywell Virtual System Release Three). It was to run on the DPS6-plus hardware known internally as the MRX and HRX, and be all things to all people.
The hardware was a dud (though it did run the native DPS6 software just fine), and the goal was, shall we say, ambitious. The effort was cancelled by Bull in 1987, in favor of another project going on in France.