How does the shift to GitHub impact project collaboration?

Social coding environments such as GitHub and Bitbucket are changing the way software is built. They are not only lowering the barriers for placing changes, but also making open-source contributions more visible and traceable. Not surprisingly, several mature, active, non-trivial open-source software projects are switching their decades of software history to these environments. There is a belief that these environments have the potential of attracting new contributors to open-source projects. However, there is little empirical evidence to support these claims. In this paper, we quantitatively and qualitatively studied a curated set of open-source projects that made the move to GitHub, aiming at understanding whether and how this migration fostered collaboration. Our results suggest that although interaction in some projects increased after migrating to GitHub, the rise of contributions is not straightforward.