Linux, also known as GNU/Linux, is a free, UNIX-like operating system, developed originally for home PCs, but which now runs on a variety of platforms including PowerPC, Macintosh, Amiga, Atari, DEC Alpha, Sun Sparc, ARM, and many others. Linux aims for POSIX compliancy to maintain maximum compatibility with other UNIX-like systems. With millions of users worldwide, Linux is probably the most popular UNIX-like OS in the world.
The Linux System
The central nervous system of Linux is the kernel, the operating system code which runs the whole computer. The kernel is under constant development and is always available in both the latest stable release and the latest experimental release. Progress on development is very fast, and the recent 2.4-series kernels are simply amazing on all counts. The kernel design is modular, so that the actual OS code is very small yet able to load whatever functionality it needs when it needs it, and then free the memory afterwards. Because of this, the kernel remains small and fast yet highly extensible, in comparison to other operating systems which slow down the computer and waste memory by loading everything all the time, whether it is needed or not.
Linux systems excel in many areas, ranging from end-user concerns such as stability, speed, and ease of use, to serious concerns such as development and networking. Nowadays, Linux even offers a variety of commercial productivity packages and office suites which can import and export files from other platforms, including Windows and MacOS.
Stability
Linux has long been praised for its stability--Linux boxes are known for running months or even years at a time without crashing, freezing, or having to be rebooted. Linux users sometimes poke fun at other, less stable operating systems, by way of screensavers like BSOD (Blue Screen of Death, which displays crash screens from various other platforms) and games like XBill (where an evil virus masquerading as a popular operating system is causing machines to catch on fire).
Linux is Y2K-compliant, storing the date in a different way from other computers. (Its trouble date is 2038, by which time a small modification to the kernel should have solved the problem.) Also, because it is extremely secure compared to other platforms, viruses for Linux are practically non-existent.
Speed
Linux machines are also known to be extremely fast, because the operating system is very efficient at managing resources such as memory, CPU power, and disk space. More of the Web than one might expect is actually powered by old 486 boxes running Linux and the Apache Web Server, while NASA, Sandia, Fermilabs and others have built very powerful yet inexpensive supercomputers by creating clusters of Linux boxes running in parallel.
Graphical Interface
As for an intuitive graphical interface, Linux has at least a dozen different, highly configurable graphical interfaces (known as window managers) which run on top of XFree86, a free implementation of the X Window System. The most popular window managers at the moment are KDE (the K Desktop Environment) and GNOME (the GNU Network Object Model Environment). These offer the point-and-click, drag-and-drop functionality associated with other user-friendly environments (for example, Macintosh), but are extremely flexible and can take on a number of different looks and feels. If you want a Linux box running KDE to look just like a Mac, Windows, BeOS, or NextStep machine, you can do it with a few mouse clicks. Today, even complex tasks like system administration, package installation, upgrading, and network configuration can be done easily through graphical programs. Programs that work with one window manager nearly always work with all the others.
Software Development
Programmers often find that the Linux development environment is second to none--a good thing for end users who depend on these software developers to provide free software. Nearly all development software for Linux is free and covered under the GNU Public License, which guarantees that it will always remain free. Linux systems come standard with C and C++ compilers and an assembler, and often include Pascal, FORTRAN, and BASIC implementations as well. In addition, modern languages like Perl and Python and classic languages like LISP are all available, fully functional and completely free. In addition, the source code for nearly any Linux program is freely available (and often included by default). This not only means that bugs are discovered and corrected almost immediately, but development of software proceeds at a much faster pace than one finds even at extremely successful commercial software houses. This phenomenon is called Open Source and is the subject of much discussion and amazement in the business world, the computer world, and the press.
Networking
Networking comes naturally to Linux. After all, Linux is based on UNIX, where computer networking more or less developed. Probably all networking protocols in use on the Internet are native to UNIX and/or Linux, so one can expect that UNIX and Linux would network better than any other platforms. Setting up a network on a Linux machine is surprisingly simple, because Linux handles most of the work; you just have to give it the correct addresses. Linux is made for networking. A large part of the Web is running on Linux boxes, especially because of the Apache Web Server which dramatically defeated its commercial competitors, proving the effectiveness and viability of the Open Source approach.
Productivity
Productivity software availability has exploded in recent years, and commercial developers have been producing excellent software for the Linux platform. Netscape Navigator and Communicator are freely available (with some licensing restrictions) as well as Word Perfect 9 and a host of others, which often come standard on Linux distributions. Today, it has become hard to keep track of all the spreadsheets, databases, and word processors. Many distributors package commercial software with their distributions, and many commercial producers offer free downloads, so even if a package has the polished quality of a professional production, you might not have to pay for it. Linux productivity packages can usually read and write files from productivity packages on other platforms; Linux has always strived for compatibility and openness. In fact, Linux is perfectly happy to coexist on the same machine as other operating systems. For example, you could install Linux, Windows, BeOS, and OS/2 all on one system! This makes it possible for new Linux users to see if they like Linux without erasing their old OS or having to buy another computer.