The ns-3 project is developing a new open source, modular network simulator, aimed at supporting top-tier research in networking. It aims to replace the venerable ns-2 simulator, which has had a profound effect on networking research but has fallen out of date with respect to models, scalability, scripting language, and alignment with current research priorities favoring better testbed integration. In the past year the ns-3 project has achieved several milestones, including its first "stable" code release. Its core capabilities include a complete discrete event manager built on sophisticated C++ object management and tracing mechanisms, full TCP/IP implementations, and several typical network device and physical layer models, including WiFi. A large and growing network of developers and followers have taken up the project, with increasing numbers of contributors and users. There are presently six known research groups advancing and validating the WiFi models, and the project is currently exceeding over 1000 downloads per month of our released software, with many additional users working directly from the development tree.