This paper adopts a systematic literature review method and a content analysis method to examine and review the current literature on open source developer forking motivation to investigate categories, research types and reports, specifically, literature in the emerging field of using forking to maintain project sustainability. The review generated five conclusions: 1) reviving original project health is important; 2) there are few frameworks on social interaction and negotiation policy between project leaders, junior and senior developers that could minimise project-to-project developer migration; 3) many papers analysed social forking community behaviour; 4) the biggest fork threat is poor guidance; and 5) most research used qualitative and statistical analyses to analyse forking activity. A methodological framework for forking sustainability is developed from the literature review. The contributions of this paper include providing a quick reference for new open source researchers to understand categories of developer forking motivation, and to introduce guidelines to open source software communities on ways to reduce organisational issues as motivating factors for developers.