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

PKUNZIP

    A program to unpack archives created by
   PKZIP, written by PKWARE, Inc. and released as
   shareware.  Versions exist for MS-DOS, Microsoft Windows
   and Open VMS.  PKUNZIP is no longer distributed, its
   functions having been incorporated into PKZIP.

   (1999-01-07)