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
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
Free SNMP Agent Simulator - Verax Systems provides applications covering the entire IT & Telco service lifecycle from definition through provisioning and monitoring up to billing.
Mininet - Mininet is a robust and inexpensive Instant Virtual Network designed to function on standard PCs like Laptops and Desktops.