ns-3 is a discrete-event network simulator for Internet systems, targeted primarily for research and educational use. ns-3 is free, open-source software, licensed under the GNU GPLv2 license, and maintained by a worldwide community.
OMNeT++ Alternatives
OMNeT++ is described as 'Modular, component-based C++ simulation library and framework, primarily for building network simulators. OMNeT++ can be used for free for non-commercial simulations like at academic institutions and for teaching' and is an app in the development category. There are 1 alternatives to OMNeT++ for Linux. The best OMNeT++ alternative is ns-3, which is free.