The Multi-Simulator Interface (MSI) is a simulation interconnection engine. It connects simulations by synchronizing their clocks and data. It is a light-weight HLA alternative.
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.