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

TYMCOM-X

    Tymshare's operating system which ran
   for many years on Tymshare's PDP-10s.  It was a descendent
   of TOPS-10 but had many of the important features of
   TOPS-20 such as real paging and controllable/spawnable
   processes.  TYMCOM-X, one of the best kept secrets in the
   PDP-10 folklore, was written by Bill Weiher, Vance Socci
   , Allen Ginzburg, Karen Kolling, Art
   Atkinson, Gary Morgenthaler (founder of the company that
   produced IDRIS), Todd Corenson and Murray Bowles.  Some
   copies still run today.  Most TYMNET development was done
   under TYMCOM-X and Tymshare sold a TYMCOM-X system to TRW to
   use in their credit reporting network, which was based on a
   purchased copy of TYMNET circa 1979.

   [E-mail from Vance Socci 1994-05-20].

   (1995-11-09)