elmer - Elmer is an open-source software package that solves partial differential equations. Combined with its ability to run various equations in parallel, it is an effective tool for running multiphysical simulations. Read more about elmer.
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
SimFlow - SimFlow is a powerful CFD software, focused on engineering and science.
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
COMSOL Multiphysics - COMSOL is the developer of COMSOL Multiphysics software, an interactive environment for modeling and simulating scientific and engineering problems.
QUCS - Qucs, briefly for Quite Universal Circuit Simulator, is an integrated circuit simulator which means you are able to setup a circuit with a graphical user interface (GUI) and simulate the large-signal, small-signal and noise behaviour of the circuit.