NecJGui is an antennas design tool, interface for Numerical Electromagnetic Code. It allows easily making NEC input files, and viewing them in 3D. It also contains a version of the simulator, so it's complete IDE for full-wave EM simulation.
** IMPORTANT NOTICE ** 10 Feb 2006 Code is being moved to the SMI subversion repository (http://smi-protege.stanford.edu/svn/owl/trunk/) Project will continue to be open source. ProtegeOWL info at: http://protege.stanford.edu/overview/protege-owl.html