Due to their characteristics and claimed advantages, several researchers have been investigating free and open-source projects. Different aspects are being studied: for instance, what motivates developers to join FLOSS projects, the tools, processes and practices used in FLOSS projects, the evolution of FLOSS communities among other things. Researchers have studied collaboration and coordination of open source software developers using an approach known as social network analysis and have gained important insights about these projects. Most researchers, however, have not focused on the integrated study of these networks and, accordingly, in their interrelationships. This paper describes an approach and tool to combine multiple social networks to study the evolution of open-source projects. Our tool, named Sargas, allows comparison and visualization of different social networks at the same time. Initial results of our analysis can be used to extend the "onion-model" of open source participation.