For now, I will give links to other Free CEM codes as well some CEM sources.
is a prominent CEM code which is being hosted at
The Clemson Vehicular Electronics Laboratory.
This isn't a free code since they do not allow for modification, only free
copying and distribution of the code. EMAP can handle 3-D elements like
bricks and tetrahedrons. I do not think they have a GUI for it yet.
gives a very good introduction to antennas and electromagnetism. They also give a
good derivation of the mathematics of a waveguide on
this page, which was very helpful in testing SLFCEM.