FlexSim - Simulation software to model, simulate, predict, and visualize systems in manufacturing, material handling, healthcare, warehousing, mining, etc.
OpenFOAM - OpenFOAM® - Official home of The Open Source Computational Fluid Dynamics (CFD) Toolbox.
ns-3 - a discrete-event network simulator for internet systems
ANSYS Fluent - ANSYS engineering simulation and 3D design software delivers product modeling solutions with unmatched scalability and a comprehensive multiphysics foundation.
Paessler Multi Server Simulator - Paessler Multi Server Simulator is inexpensive and robust software that helps you power massive-scale testing.
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming