We present CodeSaw, a social visualization of distributed software development. CodeSaw visualizes a distributed software community from two important and independent perspectives: code repositories and project communication. By bringing together both shared artifacts (code) and the talk surrounding those artifacts (project mail), CodeSaw reveals group dynamics that lie buried in existing technologies. This paper describes the visualization and its design process. We apply CodeSaw to a popular open source project, showing how the visualization reveals group dynamics and individual roles. The paper ends with a discussion of the results of an online field study with prominent open source developers. The field study suggests that CodeSaw positively affects communities and provides incentives to distributed developers. Furthermore, an important design lesson from the field study leads us to introduce a novel interaction technique for social visualization called spatial messaging.