REAL - a modular network simulator featuring a java GUI 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. 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. Scalable Networks - Network simulator designed from the outset for maximum speed and scalability, with real-time simulation as an achievable goal. BRITE - Tool for generation of realistic internet topologies, with export to several network simulators (currently ns2, JavaSim, and SSFNet). x-sim - The x-kernel protocol framework can be used as a complete simulation environment for TCP/IP 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).