YANS (Yet Another Network Simulator) is a prototype network simulator that was built to experiment and validate a new core architecture and various required functionalities for network simulation. We wanted to make it very easy to perform a number of tasks which are often regarded as very hard and sometimes impossible with NS-2 or other simulators  . YANS is built around a C/C++ simulation core that provides a simulation event scheduler, and a number of utility APIs used to implement various network models. The rest of the C/C++ code implements models for various network components. YANS also provides a default Python wrapper for the simulation core and the models bundled with it. The code for this simulator is covered by the GPLv2 license and is available through http://yans.inria.fr/ .
The YANS network simulator prototype allows us to evaluate performance of the new architecture for a possible future integration into NS-3 (http://www.nsnam.org/ ), the next generation of NS-2. The NS-3 four-year program funded as part of the NSF CISE CRI program was officially started on July 1, 2006 and we, and especially Mathieu Lacage, actively participate to the design choices and to the implementation of the new NS-3 simulator.