FREE electromagnetic simulator, i.e. emGine can be used to simulate 3D microwave devices on any platform (Windows, Linux, MacOS X). The following can be used to download

http://www.petr-lorenz.com/emgine/index.php?option=com_content&view=article&id=44&Itemid=53

You may like this:

http://slfcem.sourceforge.net/

and more in github.

Take into account that software in official repositories has been more fully tested, but experimental software may have more features.

FDTD: openEMS (http://openems.de/index.php/Tutorials) includes extensive Matlab/Octave and Python API, amny good examples, good efficiency by using an innovative FDTD formulation.

FEM: FEniCS (https://fenicsproject.org/) with Python API and some EM examples

BEM: BEM++ (http://www.bempp.org/tutorials.html) with Python API and some examples for EM

FEM and BEM Hybridization using FEniCS and BEM++(Requires good knowledge of both).

https://www.gprmax.com/