Akaroa: Akaroa is a package for supporting the Multiple Replications In Parallel (MRIP) simulation technique to harness the computing power of a network of inexpensive workstations. Integration exists with the Ptolemy Classic, ns2 and OMNeT++ simulators.
BRITE: Tool for generation of realistic internet topologies, with export to several network simulators (currently ns2, JavaSim, and SSFNet).
J-Sim: A component-based, compositional simulation environment.
NIST ATM/HFC Network Simulator:
ns2 network simulator: Ns is a discrete event simulator targeted at networking research. Ns provides substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless (local and satellite) networks.
OMNeT++: OMNeT++ is an open-source, component-based simulation package built on C++ foundations. It offers a C++ simulation class library and GUI support (graphical network editing, animation).
Parsec: a C-based simulation language for sequential and parallel execution of discrete-event simulation models
REAL: a modular network simulator featuring a java GUI
Scalable Networks: Network simulator designed from the outset for maximum speed and scalability, with real-time simulation as an achievable goal.
SSFNet: SSF (Scalable Simulation Framework) is a public-domain standard for discrete-event simulation of large, complex systems in Java and C++. Several SSF implementations and a large number of open-source protocol models and other components exist.
x-sim: The x-kernel protocol framework can be used as a complete simulation environment for TCP/IP networks.