Blender - Blender is the open source, cross platform suite of tools for 3D creation.
GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
FreeCAD - An open-source parametric 3D modeler
ns-3 - a discrete-event network simulator for internet systems
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
NetSim - NetSim software was created to simulate various Cisco systems. Cisco software is known around the world as being one of the best network, routing and switch systems for businesses and private use. Read more about NetSim.