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

STk

    A Scheme interpreter blended
   with Ousterhout's Tk package by Erick Gallesio
   .  STk expresses all of Tk as Scheme objects.
   STk includes a slow CLOS/Dylan-like object-oriented
   extension.

   STk almost conforms to R4RS and runs on SunOS 4.1.x and
   Ultrix/MIPS.

   (ftp://kaolin.unice.fr/pub/STk-1.00.tar.gz).
   (ftp://ftp.cs.indiana.edu/pub/scheme-repository/imp/STk-2.1.tar.Z).

   (2000-12-16)