Init systems are essential components of operating systems that manage the startup process and control system services. They initialize the system during booting, launching necessary processes and services, and ensuring that everything runs smoothly. Common init systems include Systemd, SysVinit, and Upstart, each with its own methods for managing services. These systems also handle service dependencies, allowing them to start in the correct order. They provide tools for monitoring and controlling services, enabling administrators to start, stop, or restart services as needed. Overall, init systems play a crucial role in maintaining system stability and performance.