Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Cisco Packet Tracer - Download Cisco Packet Tracer, an innovative network simulation and visualization tool used by Cisco Networking Academy students and instructors.
FreeCAD - An open-source parametric 3D modeler
GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
Paessler Multi Server Simulator - Paessler Multi Server Simulator is inexpensive and robust software that helps you power massive-scale testing.