GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
ns-3 - a discrete-event network simulator for internet systems
FlexSim - Simulation software to model, simulate, predict, and visualize systems in manufacturing, material handling, healthcare, warehousing, mining, etc.
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.
Paessler Multi Server Simulator - Paessler Multi Server Simulator is inexpensive and robust software that helps you power massive-scale testing.
Ranplan Wireless - Ranplan Wireless is a leading platform that has revolutionized itself with innovative wireless tools and software based on extensive technology.