J-Sim
- A component-based, compositional simulation environment.
- http://www.j-sim.org/

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.
- http://www.cosc.canterbury.ac.nz/research/RG/net_sim/simulation_group/akaroa/

BRITE
- Tool for generation of realistic internet topologies, with export to several network simulators (currently ns2, JavaSim, and SSFNet).
- http://www.cs.bu.edu/brite/

Scalable Networks
- Network simulator designed from the outset for maximum speed and scalability, with real-time simulation as an achievable goal.
- http://www.scalable-networks.com

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.
- http://www.isi.edu/nsnam/ns/

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).
- http://www.hit.bme.hu/phd/vargaa/omnetpp.htm

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.
- http://www.ssfnet.org/

x-sim
- The x-kernel protocol framework can be used as a complete simulation environment for TCP/IP networks.
- http://www.cs.arizona.edu/xkernel/

Parsec
- a C-based simulation language for sequential and parallel execution of discrete-event simulation models
- http://may.cs.ucla.edu/projects/parsec/

REAL
- a modular network simulator featuring a java GUI
- http://www.cs.cornell.edu/skeshav/real/overview.html