Ansoft Maxwell

From their website:

ANSYS Maxwell is the premier low-frequency electromagnetic field simulation software for designing and analyzing 3-D and 2-D electromagnetic and electromechanical devices. Engineers use Maxwell to accurately design all types of industrial devices including motors, actuators, transformers, MRI coils, sensors, power supplies and more. http://www.ansys.com/Products/Simulation+Technology/Electronics/Electromechanical/ANSYS+Maxwell

Labs

Maxwell is available under Linux.