Horizontal 4-Wheel Independent Steering (4WiS) is a next-generation steering system that independently controls all four wheels to deliver unprecedented vehicle maneuverability, stability, and motion control. The system combines horizontally packaged steering actuators with an independent rack-bar architecture, enabling software-defined optimization of vehicle dynamics. At low speeds, it significantly reduces turning radius for superior maneuverability, while at high speeds it enhances stability, handling, and driving confidence. A key innovation of Horizontal 4WiS is its horizontal actuator packaging concept, which enables seamless integration into mass-production vehicle platforms, including both internal combustion engine and electric vehicles. In addition, its fail-operational architecture maintains steering functionality even in the event of a failure in one or more actuators, ensuring continuous control and safety. More than a steering technology, Horizontal 4WiS serves as a scalable mobility platform that integrates steering, software-defined vehicle motion control, and fail-operational safety, creating a foundation for future autonomous and software-defined mobility.