The most popular open-source operating system is Linux. Known for its stability, security, and flexibility, Linux serves as the foundation for numerous distributions, such as Ubuntu, Fedora, and Debian. It is widely used in server environments, cloud infrastructure, and as an operating system for many devices, from smartphones to embedded systems. The open-source nature of Linux allows developers to modify and distribute the source code, fostering a large community that contributes to its continuous improvement and expansion across diverse technological landscapes.