Hello,
the FORMAT package works with Maxima (I include it in Symaxx by default).
Only the installation is a bit tricky. My way of getting it to work (which
may or may not be the easiest way) is to copy the files to a location, where
Maxima finds then, and then to 'compile_file' format.lisp and coeflist.lisp
once by hand.
When this is done, the package is loaded with
loadfile("format.o")
loadfile("coeflist.o").
Test it for example with
format(expand((x+y)^6),%poly(x)).
Regards
Markus