1960s, two approaches to improve production emerged: automation and augmentation. Until recently, physical and mechanical automation dominated industrial research. However, with the emergence of the Fourth Industrial Revolution, the potential of Human-Computer Interaction (HCI) serving a transformative role in manufacturing has gained significant interest and relevance in industry. Where full automation is ineffective or infeasible, Operator Assistance Systems (OAS) can augment workers' cognitive or physical capabilities. In this monograph, the authors frame OAS as a subset of HCI systems designed for the purpose of workforce augmentation in production systems. However, while OAS are anticipated to address key needs in industry, a challenge for both OAS researchers and industrial practitioners is to identify the most promising applications of OAS and justify them from a value-added perspective. This monograph addresses the challenges in OAS by presenting a systematic literature review revealing 11 application areas for OAS and 12 approaches for assessing the value-added of OAS. The authors also discuss implications for OAS, with a particular focus on integration in industry.