The Free On-line Dictionary of Computing (30 December 2018):

On-line Process Synthesizer

    (OPS) A system for discrete simulation under
   CTSS developed by M. Greenberger at MIT ca. 1964.

   [Sammet 1969, p.660. Versions: OPS-3, OPS-4. "On- line
   Computation and Simulation: The OPS-3 System", M. Greenberger
   et al, MIT Press 1965].

   (2003-04-05)