This paper studies the success of Open Source Software (OSS) projects in attracting developer interest and achieving project efficiency. The focus of our study is on examining the relationship between the four sets of capabilities proposed in the Theory of Competency Rallying (TCR) and the success of OSS projects. The data collected from 607 OSS projects mainly confirm that the capabilities proposed in the TCR are necessary for the success of OSS projects. The results of this study show that in order to succeed, OSS projects should constantly identify their market's quality and functionality needs. Ability of OSS project managers to know which developers possess certain skills required to meet a particular market need is also found to be critical. Another capability that is recognised to be crucial in predicting project success is the ability of OSS developers in effectively addressing market needs and continuously learning from such experiences. Finally, the ability of stakeholders involving in addressing a particular market need to efficiently collaborate and fulfil that specific market need is found to be another essential capability required for OSS projects to succeed. Implications of the results for practitioners and the research community are presented.