Linux

Linux is a family of open-source Unix-like operating systems based on the Linux kernel, which is created by Linus Torvalds in 1991.

Operating systems based on Linux are called Linux distributions. Many of them include the GNU software suite (except distributions such as Android). They also include their own package managers and other implementations of things.

In the OSM community, Linux, like macOS and other real OSes, are less popular than Windows.