Open source is playing an increasingly important role in the software and communications industries. In particular, open source implementations are widely available for most Internet protocols, from kernel-resident Ethernet drivers, WLAN drivers, and TCP/IP stacks (e.g., in Linux, BSD, and Android operating systems) up to user-space networked applications (e.g., web clients and proxies). Open sourced applications are arguably becoming more prevalent than proprietary closed software. Hundreds of open source networking packages have played important roles in our daily life. The same open source spirit also goes to some medium access control (MAC)/physical (PHY) hardware components and the development platforms for simulation, rapid prototyping, software defined radio, and software defined networking.