Paessler Multi Server Simulator - Paessler Multi Server Simulator is inexpensive and robust software that helps you power massive-scale testing.

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.

VNX - VNX is a simple, fast, and highly effective virtualization tool developed to assist you in creating virtual network testbeds automatically, resulting in time-saving.

Mininet - Mininet is a robust and inexpensive Instant Virtual Network designed to function on standard PCs like Laptops and Desktops.

IMUNES - IMUNES is a cost-effective and efficient Integrated Multiprotocol Network Simulator/Emulator that functions as a tool for Linux and FreeBSD.