OMNeT++
OMNeT++ is an extensible, modular, component-based C++ simulation library and framework, primarily for building network simulators. Network in this case is meant in a broader sense that includes wired and wireless communication networks, on-chip networks, queueing networks,
OMNeT++ provides a component architecture for models. Components (modules) are programmed in C++, then assembled into larger components and models using a high-level language (NED)
OMNeT++ is not a simulator in itself but rather a simulation framework. Instead of containing explicit and hardwired support for computer networks or other areas, it provides the infrastructure for writing such simulations. Specific application areas are catered by various simulation models and frameworks, most of them are open source. These models are developed completely independently of OMNeT++, and follow their own release cycles.
OMNeT++ is released with full source code, and is free to use, modify and distribute in academic and educational institutions under its own license (Academic Public License). Corporate use requires, however, a paid license of OMNEST.