From Active to Zombie: A Literature Review on Bus Factor's Role in Open Source Project Lifecycle Decline

Abstract

Open Source Software (OSS) has become critical global digital infrastructure, yet its sustainability remains profoundly threatened by the concentration of knowledge within small cohorts of core developers a vulnerability formally quantified as the Bus Factor. This systematic literature review examines the role of Bus Factor dynamics in driving OSS projects toward the zombie phase, a deceptive intermediate state wherein repositories remain administratively active while genuine human-driven development has ceased. Following a PRISMA-based selection process across Google Scholar, Semantic Scholar, and the ACM Digital Library, 14 peer-reviewed studies were identified, quality-assessed, and thematically categorized to answer four research questions concerning Bus Factor measurement, lifecycle decline, computational prediction methods, and contributor behavioral dynamics. The review traces the evolution of Bus Factor measurement across four methodological generations and constructs a formal causal framework linking knowledge concentration to project death via sleeping developer behavior and zombie phase onset. Empirical evidence confirms that 89.65% of OSS projects experience total core developer loss, with only 27.07% recovering successfully. Critically, dynamic Bus Factor fluctuation remains entirely absent from existing abandonment prediction models. This review identifies this absence as the central research gap and identifies several candidate methodological directions for future empirical investigation. These findings establish a cohesive theoretical framework to guide proactive OSS sustainability research.