The term “open source software” was formally introduced in the early 2000s to describe source code which are available to the public to be used and modified by anyone. Like any innovative idea attaining a certain maturity level, open source communities have reached a degree of formalization in their structures and practices. This also holds for knowledge management and its related measures in open source communities. Therefore, we investigate the patterns and structures in communication and collaboration of the currently most successful open source software projects through a case study approach. Herewith, we reveal how the different knowledge management aspects are practiced in these internet communities. Due to the projects’ success, we identify similarities as good practices and derive practical recommendations for action for other open source communities as well as research opportunities regarding knowledge management in open source software projects.