Twenex

 TWENEX n. The TOPS-20 operating system by DEC. So named because
       TOPS-10 was a typically crufty DEC operating system for the PDP-10.
       BBN developed their own system, called TENEX (TEN EXecutive), and in
       creating TOPS-20 for the DEC-20 DEC copied TENEX and adapted it for
       the 20. Usage: DEC people cringe when they hear TOPS-20 referred to as
       "Twenex", but the term seems to be catching on nevertheless.
       Release 3 of TOPS-20 is sufficiently different from release 1 that
       some (not all) hackers have stopped calling it TWENEX, though the
       written abbreviation "20x" is still used.