FEATool Multiphysics is an easy-to-use FEA and CFD Simulation Toolbox
VHDL Verification and Simulation Tool
OpenNum lets you distribute solvers with a nice graphical interface
PySCeS Constraint Based Modelling
A Library for Interactive Modelling and Visualisation
GDS visualization and parallelized capacitance extraction
PyParticles is an opensource particles simulation tool box entirely wr
Python-based GUI for discrete-event system modeling and simulation