MEEP
Background
Meep (or MEEP) which stands for MIT Electromagnetic Equation Propagation, is a free finite-difference time-domain (FDTD) simulation software package developed at MIT to model electromagnetic systems.
Meep is written in C++, there is two main interfaces that are the most used (libctl/scheme). C++ provides the interfaces with the greatest level of flexibility in designing FDTD simulations. Although the foundations are built in C++ you do not need to be a real programmer to use Meep.