Linus Torvalds, from Finland, released an operating system kernel under the name Linux in 1991. The word is a composition of his first name and the underlying model, Unix. This basic interface between software and hardware was, and still is, used as a basis for a variety of operating systems, which are often denoted as Linux. In addition to the free licensed Linux kernel, the Linux operating systems are mostly based on freely available GNU software. The kernel and software package are also called distributions and continue to be popular among developers. This is because they are quickly distributed and can also be adjusted to as needed. In addition to the Linux kernel and free software programs, the distributors can add proprietary applications to the packages, e.g. Adobe Reader, as well as self-created programs (proprietary or free).
Throughout the years, countless distributions and their derivatives have been released this way. Debian, Ubuntu (its derivative), Mint, Gentoo, Fedora, Red Hat (Enterprise), openSUSE, and the smartphone system, Android, are among the most well-known Linux operating systems.