Thanks to the unique advantages such as long life cycles, high power density and quality, and minimal environmental impact, the flywheel/kinetic energy storage system (FESS) is gaining steam recently. There is noticeable progress made in FESS, especially in utility, large-scale deployment for the electrical grid, and renewable energy applications. This paper gives a review of the recent developments in FESS technologies. Due to the highly interdisciplinary nature of FESSs, we survey different design approaches, choices of subsystems, and the effects on performance, cost, and applications. This review focuses on the state of the art of FESS technologies, especially for those who have been commissioned or prototyped. We also highlighted the opportunities and potential directions for the future development of FESS technologies.