PI:
   PI is an interface between Prolog applications and the X Window System
   that aims to be independent from the Prolog engine, provided that it
   has a Quintus-style foreign function interface (such as SICStus, YAP).
   It is mostly written in Prolog and is divided in two libraries: (1)
   Edipo, a low-level interface to the Xlib functions, and (2) Ytoolkit,
   a high-level user interface toolkit that allows you to create and
   manage graphical objects, define new classes of objects, and handle
   user interaction. PI is available by anonymous ftp from
   ftp://ftp.ncc.up.pt/pub/prolog/ and includes documentation
   and some demos. Also see ytoolkit.tar.Z. PI has been tested in
   Quintus Prolog 3.1.1 and SICStus 2.1 #8. Send questions, comments,
   and bug reports to Ze' Paulo Leal, Universidade de Porto, Portugal,
   <zp@ncc.up.pt>. 

XWIP: 
   ftp.x.org:/contrib/xwip.tar.Z  (formerly export.lcs.mit.edu)
   ftp://ftp.uu.net/X/contrib/

   XWIP is an X Windows interface for PROLOG.

XPCE:
   XPCE is an object-oriented X-window interface toolkit for symbolic
   programming languages (Prolog and Lisp), offering a high level of
   abstraction for communication with X11, Unix processes, Unix
   networking facilities (sockets) and Unix files. XPCE's built-in
   classes (about 150) are mostly written in C.  The XPCE/Prolog
   interface allows the user to create and manipulate instances of these
   classes.  The user can also create new XPCE classes from Prolog.
   XPCE's window related classes provide various styles of menus,
   primitive graphical objects, compound graphical objects and Emacs
   oriented programmable text manipulation windows. The distribution
   contains several demo programs, including a diagram drawing tool
   (PceDraw), an animation demo, an Epoch-like editor, a graphical
   interface to Unix ispell, and an online hyper-text manual for XPCE
   itself.  A demo version of XPCE/SWI-Prolog for Linux may be obtained
   by anonymous ftp from ftp://swi.psy.uva.nl/pub/xpce/linux/ [145.18.114.17].
   The non-demo versions (for SWI-Prolog, SICStus Prolog, Lucid Common
   Lisp and LispWorks) require filling out a license and paying a fee
   (see the file pub/xpce/INFO).  To be added to the mailing list
   xpce@swi.psy.uva.nl send mail to xpce-request@swi.psy.uva.nl. Send
   bugs to xpce-bugs@swi.psy.uva.nl. 

   ProWindows 3 is a commercial version of XPCE for Quintus Prolog. 
   For further information, write to Simon Heywood, AI International Ltd, 
   The Chapel, Park View House, 1 Park View Road, Berkhamsted, Herts, 
   HP4 3EY, phone +44-(0)442-876722 (Sales Hotline +44 (0)442 876448),
   fax +44-(0)442-877997, or send email to sheywood@aiil.co.uk.

ProTcl:

   ProTcl (pronounced pro-tickle) is a Prolog interface to Tcl/Tk. It has
   a very simple and lightweight interface, which allows one to evaluate
   Tcl expressions from Prolog. It defines the tcl_eval/1,2 predicate
   which passes the Tcl expressions to the Tcl interpreter. It has been
   tested on ECLiPSe and SICStus, on a Sparc 10. ProTcl is available
   by anonymous ftp from 
      ftp://ftp.ecrc.de/pub/eclipse/progs/protcl/
   The ProTCL home page is
      http://www.ecrc.de/eclipse/html/protcl.html
   Send comments and suggestions to Micha Meier <micha@ecrc.de>.