Linux is a family of free and open-source Unix-like operating systems based on the Linux kernel, which was first released on 17 September 1991 by Linus Torvalds. Some members of the family are typically packaged as a distribution, which includes the kernel alongside supporting system software and libraries developed by third parties—such as GNU, Red Hat, and X.Org—to create a complete operating system; however, not all Linux-based operating systems are considered distros, with Android being an example. Linux was originally designed as a clone of Unix and is distributed under the copyleft GPL license. There are many thousands of Linux distributions, many based directly or indirectly on other distributions; popular Linux distros include Debian, Fedora Linux, Linux Mint, Arch Linux, and Ubuntu, while commercial distributions include Red Hat Enterprise Linux, SUSE Linux Enterprise, and ChromeOS. Linux distributions are frequently used in server platforms.