Linux is a remarkably complete operating system, including a graphical user interface, X Window System, TCP/IP, the Emacs editor, and other components usually found in a comprehensive UNIX system. Although copyrights are held by various creators of Linux's components, Linux is distributed using the Free Software Foundation's copyleft stipulations that mean any copy is in turn freely available to others.
Unlike Windows and other proprietary systems, Linux is publicly open and extendible by contributors. Because it conforms to the POSIX standard user and programming interfaces, developers can write programs that can be ported to other operating systems, including IBM's OS/390 running UNIX. Linux comes in versions for all the major microprocessor platforms including the Intel, PowerPC, Sparc, and Alpha platforms.
Linux is distributed commercially by a number of companies. A magazine, Linux Journal, is published as well as a number of books and pocket references.
Linux is sometimes suggested as a possible publicly-developed alternative to the desktop predominance of Microsoft Windows. Although Linux is popular among users already familiar with UNIX, it remains far behind Windows in numbers of users.