The process and activities of software development are very dynamic and diverse. For instance, source code has to be written, tested and revised, e-mails have to be sent, bugs have to be communicated, managed and fixed. As a consequence, the contributions of the developers are very diversified. This paper describes an empirical study whose goal was to assess and compare the contributions of the developers through software repository mining. Two medium-sized projects - an open source and a commercial project - were analyzed. Overall, 17,490 commits and 10,308 bugs reports were analyzed. In the first part of our study, we have classified the developers based on their contribution to the software repository in three groups - core, active and peripheral developers. After that, we have collected a series of metrics - code contribution, buggy commits and resolution of priority bugs - for all the developers of the investigated projects. Finally, we have analyzed the collected metrics for the different developer groups. Our study findings show significant differences in the contribution provided by the developers groups considering the open-source and the commercial project.