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

Quintus Prolog

    A version of Prolog developed by
   Quintus.  Development of Quintus Prolog had transferred to
   the Swedish Institute of Computer Science by December 1998.

   (ftp://ftp.quintus.com/).

   Telephone: +1 (800) 542 1283.

   [More details?  Features?]

   (1998-12-12)