GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
AnyLogic - AnyLogic has changed simulation modeling and expanded its application into complex business environments. The unmatched flexibility of multimethod modeling allows users to capture the complexity of virtually any system, at any level of detail.
Cisco Packet Tracer - Download Cisco Packet Tracer, an innovative network simulation and visualization tool used by Cisco Networking Academy students and instructors.
ns-3 - a discrete-event network simulator for internet systems
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