Johan Bevemyr's Luther-based WAM-tracer is available by anonymous ftp
from Uppsala University in Sweden. It includes a simple compiler from
Prolog to WAM code and a low-level WAM code tracer written in
emacs-lisp.  The tracer splits the screen into regions to show
data-areas, registers, and so on. You can then step through running
the code. The tracer is available by anonymous ftp from
   ftp.csd.uu.se:/pub/WAM-tracer/luther.tar.Z
Documentation on the tracer is included in the distribution.  The
emulator is in the /pub/WAM-emulator/ directory (and runs in SICStus
Prolog).  For more information, contact Johan Bevemyr
<bevemyr@csd.uu.se> or <bevemyr@sics.se>.