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.
Cisco Packet Tracer - Download Cisco Packet Tracer, an innovative network simulation and visualization tool used by Cisco Networking Academy students and instructors.
GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
IMUNES - IMUNES is a cost-effective and efficient Integrated Multiprotocol Network Simulator/Emulator that functions as a tool for Linux and FreeBSD.
Cisco VIRL - Cisco VIRL is a next-gen network virtualization and orchestration platform that enables you to accomplish multiple tasks like creating and customizing simulated networks with third-party and Cisco objects by means of a graphical utility.