I took a look at xcas, which is a graphical front end for giac, at:
http://www-fourier.ujf-grenoble.fr/~parisse/giac.html
There is a pdf there, for the tutorial, in french, which shows
(http://www-fourier.ujf-grenoble.fr/~parisse/tutoriel.pdf)
its gui. I think, (and my ability to read french is limited)
that the front end has the ability to accept input in
maple and mupad syntax.
Now while I realize it's not written in lisp, it is a front end
that is gpl'd.
Comments?