<p>The adoption of Variable Frequency Clock (VFC) in different application-specific integrated circuits (ASICs) has gained popularity over the decades because of its flexibility and adaptability across domains in contrast to any conventional clocking system. This paper presents a detailed study of VFCs, exploring their classifications, operating principles, and performance metrics. Various architectures are discussed in terms of fundamental principles of programmable frequency synthesizers which are the core of VFC generation. After highlighting the advantages, limitations and design challenges of each architecture, this survey extensively explores the broader area of applications of VFC spanning to Supply Noise Management, Temperature Management, Power Management, Data Rate synchronization, and electromagnetic interference (EMI) reduction etc. Additionally, the survey provides insights into the future potential applications of VFC. By presenting a comprehensive understanding, this paper seeks to guide researchers to develop innovative, more adaptable and high-performance architectures of VFC to meet the need of evolving technological landscapes. To our knowledge, this is the first survey to unify scattered, application-specific VFC architectures into a comparative study and assess their cross-domain applicability.</p>