The best free alternative to COMSOL Multiphysics is Elmer, which is also Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to COMSOL Multiphysics and many of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to COMSOL Multiphysics are CAD Sketcher, FEATool Multiphysics, Xcos and OpenModelica.
COMSOL Multiphysics alternatives are mainly 3D Modelers, but if you're looking for
Circuit Simulators or CAD Software you can filter on that. Other popular filters include
Open Source and
Free. These are just examples - use the filter bar below to find more specific alternatives to COMSOL Multiphysics.