Context: Open-Source Software (OSS) development has gained popularity in the last two decades, having major research in the areas of OSS evolution, adoption, and development. Multiple Systematic Literature Reviews (SLR) and Systematic Mapping Studies (SMS) are published in the OSS domain; however, many areas are still open for research. Objective: The study aims to aggregate and classify Open-Source Software (OSS) research areas, topics, and, future directions. Method: A systematic tertiary study is performed to cover all the systematic secondary studies in the area of OSS. The guidelines of Kitchenham are used for designing the protocol and piloting it before execution. Result: We identified sixty studies that consist of 18 SMS and 42 SLR. The literature is mapped to an already published taxonomy of OSS by Aksulu and Wade, however, the future directions are thematically analyzed. The results of key research areas mapped to taxonomy show that the highest number of studies are in the “ OSS categorization/research agenda” . Eigth studies are mapped to “ OSS Vs Proprietary”. These studies fall in main category of “ Conceptual” The second major work is in “ OSS Production” category in the sub-categories of “ Communities”, “ User and Developer Motivation”, “ Process” and, “ Self-Organization (Product and Community Evolution)” The findings are also mapped to taxonomy. The areas that have major future directions (thematically analyzed) are OSS contributors which are “ OSS developers / OSS communities and organizations involved with OSS”, OSS evolution and prediction, use of OSS in different domains, OSS adoption/adaptation/integration, OSS process, and OSS quality. Conclusion: The mapping of key research areas to taxonomy shows that there is a lot of research potential in the OSS categories having less or no studies mapped to the. Furthermore, the explicit future directions identified thematically will also help researchers conduct future research in open source domain.