OMNeT++ is a public-source, component-based, modular and
open-architecture simulation environment with strong GUI
support and an embeddable simulation kernel. Its primary
application area is the simulation of communication
networks and because of its generic and flexible
architecture, it has been successfully used in other
areas like the simulation of IT systems, queueing
networks, hardware architectures and business processes
as well. OMNeT++ is rapidly becoming a popular
simulation platform in the scientific community as well
as in industrial settings. Several open source
simulation models have been published, in the field of
internet simulations (IP, IPv6, MPLS, etc), mobility and
ad-hoc simulations and other areas.

OMNeT++ is free for academic and non-profit use;
commercial users must obtain a license from Omnest Global Inc.

WWW: http://www.omnetpp.org/