  Motivation: Society's dependence on Open Source Software (OSS) and the
communities that maintain the OSS is ever-growing. So are the potential risks
of, e.g., vulnerabilities being introduced in projects not actively maintained.
By assessing an OSS project's capability to stay viable and maintained over
time without interruption or weakening, i.e., the OSS health, users can
consider the risk implied by using the OSS as is, and if necessary, decide
whether to help improve the health or choose another option. However, such
assessment is complex as OSS health covers a wide range of sub-topics, and
existing support is limited. Aim: We aim to create an overview of
characteristics that affect the health of an OSS project and enable the
assessment thereof. Method: We conduct a snowball literature review based on a
start set of 9 papers, and identify 146 relevant papers over two iterations of
forward and backward snowballing. Health characteristics are elicited and coded
using structured and axial coding into a framework structure. Results: The
final framework consists of 104 health characteristics divided among 15 themes.
Characteristics address the socio-technical spectrum of the community of actors
maintaining the OSS project, the software and other deliverables being
maintained, and the orchestration facilitating the maintenance. Characteristics
are further divided based on the level of abstraction they address, i.e., the
OSS project-level specifically, or the project's overarching ecosystem of
related OSS projects. Conclusion: The framework provides an overview of the
wide span of health characteristics that may need to be considered when
evaluating OSS health and can serve as a foundation both for research and
practice.
