Chez Scheme is a complete implementation of the language of the
Revised^6 Report on Scheme (R6RS), with numerous extensions.  It
sports a fast compiler that generates native code for x86, x86_64, and
32-bit PowerPC architectures.  Formerly a commercial product, it was
open-sourced by Cisco Systems in April 2016.

The unthreaded version is built by default, but enabling support for
multithreading is easy:
  THREADED=yes sh ./ChezScheme.SlackBuild

The full testing battery can also be run after the build completes:
  TEST=yes sh ./ChezScheme.SlackBuild