|Tux the penguin, the Linux mascot
|Developer: The Open Source community
|OS family: Unix-like
|Source model: Open source
|Latest stable release: Kernel 188.8.131.52 / Jul 10 2007
|Supported platforms: x86, x86-64, ia64, DEC Alpha,
Motorola 68k, SUN Sparc, ARM, PowerPC
|Kernel type: Monolithic kernel
|Default user interface: Command line
|License: GNU General Public License
|Working state: Current
The Linux kernel is the "traffic cop" of Linux, the part of the operating system that controls processes, manages memory, and loads drivers. The first Linux kernel was implemented by Linus Torvalds, a Finnish software student. Torvalds started work on Linux to provide a free Unix-like alternative to the Minix operating system, owned and developed by eminent Professor Andrew Tanenbaum. Both Linux and Minix share the distinction of running on an Intel x86 chip architecture, which before this time was dominated mainly by Microsoft's DOS and Windows. The advent of Linux made available to the public a free alternative to Windows, which also ran on the exact same low-cost hardware. Linux advocates praise it for being relatively stable and secure and quite low-cost.
The Linux kernel is a free, Unix-like, open source project licensed under the GNU General Public License. Specifically, version 2.0 of the GPL is applied to the kernel, without the "or any future versions" clause. This was an intentional move by Torvalds, and ties the kernel directly to version 2.0 of the GPL.
The Linux kernel was created in April 1991  by a Finnish software engineer named Linus Torvalds, and is now maintained largely by the community. On August 25th 1991 Torvalds posted publicly on USENET the first post describing "a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones."
Torvalds' project soon grew in popularity as a free alternative to Minix. He now acts more as a 'Benevolent Dictator for Life' and coordinates patches and improvements to the kernel, rather than directly hacking source code himself.
Much like its predecessor Unix, the Linux kernel is written in the C programming language, as well as some architecture-specific assembly to increase performance on specific processors. The design of the kernel is Monolithic, with the ability to load modules on the fly (modules are usually thought of as drivers in the Windows world). The current release holds more than 40 megabytes of source code, contributed by more than a thousand hackers.
The kernel was originally written with only the Intel 386 processor in mind. (Linus stated that he wrote the OS as a lesson in the architecture of the 386). That limitation has since been overcome, and it has since been ported to many different architectures on many different platforms, even surpassing the traditional Unix that is known to "run on anything," NetBSD.
Portability and Stability
Initially developed and used primarily by individual enthusiasts on personal computers, Linux has since gained the support of corporations such as IBM, Sun Microsystems, Hewlett-Packard, and Novell, Inc., and has risen to prominence as an operating system for servers; Netcraft reported in September 2006 that seven of the ten most reliable Internet hosting companies run Linux on their web servers. 
The current version of the Linux kernel is 184.108.40.206 as of March 2007. The first number refers to the kernel version. The Linux kernel has been on version 2 since 1996. The second number is called the major version number. It has been major version 6 since December 2003. The third number is the minor revision, and reflects the addition of drivers or features to the kernel. It is changed much more frequently than the first two numbers. The fourth number is sometimes used in the event of bug fixes or security updates of a critical nature, while an odd number denotes a developmental version.
Common Examples of Linux Distributions
The Linux kernel is most often found in a collection of software known as a Linux distribution, examples being Ubuntu, Fedora Core, and SUSE. Distributions provide an easier method of running Linux than compiling the kernel and other software from scratch, enabling users with minimal computer knowledge to run a Linux system.