One opportunity for organizations to participate in open source software (OSS) development is throughorganizations OSS(orgsOSS), a term we use to describe a group of organizations that commit resources to collectively develop OSS. This archetype of OSS development is distinct from other types that include organizations, yet is understudied. As organizations increasingly contribute to and rely on OSS as part of their strategy, understanding how they can collaborate to build software holds importance for the future of software development. This study collects a unique dataset of development tasks from a large orgsOSS project spanning over two years and seven releases. Building on existing OSS research, we explore norms with respect to collaboration, i.e., how developers assign, discuss, and complete tasks, in an orgsOSS project. Interestingly, our analysis reveals that developers in orgsOSS do not always adhere to ideals of widespread sharing and participation espoused by traditional OSS, however some developer and task characteristics helped foster these ideals. Based on these and other findings, we develop a set of propositions and associated collaboration mechanisms that are important to future orgsOSS and other similarly structured software development projects.