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GNU计划，又称革奴计划，是由RichardStallman在1983年9月27日公开发起的。它的目标是创建一套完全自由的操作系统。RichardStallman最早是在net.unix-wizards新闻组上公布该消息，并附带一份《GNU宣言》等解释为何发起该计划的文章，其中一个理由就是要“重现当年软件界合作互助的团结精神”。
　　GNU是“GNU's NotUnix”的递归缩写。Stallman宣布GNU应当发音为Guh-NOO以避免与new这个单词混淆（注：Gnu在英文中原意为非洲牛羚，发音与new相同）。UNIX是一种广泛使用的商业操作系统的名称。由于GNU将要实现UNIX系统的接口标准，因此GNU计划可以分别开发不同的操作系统部件。GNU计划采用了部分当时已经可自由使用的软件，例如TeX排版系统和X Window视窗系统等。不过GNU计划也开发了大批其他的自由软件。
　　为保证GNU软件可以自由地“使用、复制、修改和发布”，所有GNU软件都在一份在禁止其他人添加任何限制的情况下授权所有权利给任何人的协议条款，GNU通用公共许可证（GNU General PublicLicense，GPL）。这个就是被称为“反版权”（或称Copyleft）的概念。
　　1985年Richard Stallman又创立了自由软件基金会（FreeSoftwareFoundation）来为GNU计划提供技术、法律以及财政支持。尽管GNU计划大部分时候是由个人自愿无偿贡献，但FSF有时还是会聘请程序员帮助编写。当GNU计划开始逐渐获得成功时，一些商业公司开始介入开发和技术支持。当中最著名的就是之后被Red Hat兼并的CygnusSolutions。
　　到了1990年，GNU计划已经开发出的软件包括了一个功能强大的文字编辑器Emacs，C语言编译器GCC，以及大部分UNIX系统的程序库和工具。唯一依然没有完成的重要组件就是操作系统的内核(称为HURD)。
　　1991年LinusTorvalds编写出了与UNIX兼容的Linux操作系统内核并在GPL条款下发布。Linux之后在网上广泛流传，许多程序员参与了开发与修改。1992年Linux与其他GNU软件结合，完全自由的操作系统正式诞生。该操作系统往往被称为“GNU/Linux”或简称Linux。（尽管如此GNU计划自己的内核Hurd依然在开发中，目前已经发布Beta版本。）
　　许多UNIX系统上也安装了GNU软件，因为GNU软件的质量比之前UNIX的软件还要好。GNU工具还被广泛地移植到Windows和Mac OS上。
　　GNU 包含3个协议条款，
　　GPL：GNU通用公共许可证（GNU General Public License）
　　LGPL：GNU较宽松公共许可证 (GNU Lesser General Public License）, ) ，旧称 GNU Library General Public License (GNU 库通用公共许可证)；
　　GFDL ： GNU自由文档许可证（GNU Free Documentation License ）的缩写形式。
　　这里指的自由，并不是价格免费，这和价格无关而是使用软件对所有的用户来说是自由的。GPL 通过如下途径实现这一目标：
　　1.它要求软件以源代码的形式发布，并规定任何用户能够以源代码的形式将软件复制或发布给别的用户。
　　2.如果用户的软件使用了受 GPL 保护的任何软件的一部分，那么该软件就继承了 GPL 软件，并因此而成为 GPL 软件，也就是说必须随应用程序一起发布源代码。
　　3.GPL 并不排斥对自由软件进行商业性质的包装和发行，也不限制在自由软件的基础上打包发行其他非自由软件。
　　由于GPL很难被商业软件所应用，它要求调用它的库的代码也得GPL，全部开放，并且一同发布，不能直接连接。所以后来GNU推出了LGPL许可证
　　如果你准备在你的项目中使用Linux,那么你必须了解的两个上述两个两个许可证，GPL与LGPL..
　　相同点：
　　因为GPL和LGPL，都是自由软件基金会建立的，所以它们之间非常类似，它们都具备Copyleft的重要特性：
　　术语copyleft源于GNU项目中的俗语，是英语Copyleft的双关语（Copyright：版权），表示反版权，也就是非盈利版权的意思。他指的是开放源代码许可证中如下条款：任何人或者公司都不能把GPL/LGPL保护下的软件源代码拷贝，修改后，把这些修改保护起来——即使他们的修改可能使得软件的性能比原始的版本更好。一旦一段代码被GPL或者LGPL保护，那么代码本身和所有对它所做的修改都必须在对它感兴趣的人和组织面前公开，如果第三方修改并发布这段代码，那么必须把修改的代码和原始代码都向接受代码的人公开。
　　不同点：
　　在GPL与LGPL许可证保护下发布源代码的结果很相似，对旧代码所做的任何修改对于想知道这些代码的人必须是公开的，唯一真正的不同之处在于私人版权代码是否可以与开放源代码相互连接，LGPL允许实体连接私人代码到开放源代码，并可以在任何形式下发布这些合成的二进制代码。只有这些代码是动态连接的就没有限制。（使用动态链接时，即使是程序在运行中调用函数库中的函数时，应用程序本身和函数库也是不同的实体）
　　GNU (pronounced /gnu/) is a free softwareoperating system. Its name is a recursive acronym for "GNU's Not Unix",which was chosen because its design is Unix-like, but it contains noactual UNIX code. The GNU system, combined with a third-party kernelcalled Linux, is one of the most widely used operating systems in theworld known as "GNU/Linux". The plan for the GNU operating system wasannounced in September 1983 by Richard Stallman and softwaredevelopment work began in January 1984. The project to develop GNU isknown as the GNU Project, and programs released under the auspices ofthe GNU Project are called GNU packages or GNU programs.
　　History
　　The GNU project was announced publicly onSeptember 27, 1983, on the net.unix-wizards [1] and net.usoftnewsgroups. Software development began on January 5, 1984, whenStallman quit his job at Massachusetts Institute of Technology so thatthey could not claim ownership or interfere with distributing GNU asfree software. The correct pronunciation of GNU is g'noo (IPA: /gnu/),with a hard "g", to distinguish it from the word new. According toStallman, the name was inspired by various plays on words, includingthe song The Gnu.
　　The goal was to bring a wholly freesoftware operating system into existence. Stallman wanted computerusers to be free - as most were in the 60s and 70s - free to study thesource code of the software they use, free to modify the behaviour ofthe software, and free to publish their modified versions of thesoftware. This philosophy was published in March 1985 as The GNUManifesto.
　　The majority of the software needed had tobe written from scratch, but when compatible free software componentsalready existed, they were used. Two examples were the TeX typesettingsystem, and the X Window System. Most of GNU has been written byvolunteers; some in their spare time, some paid by other companies. InOctober 1985, Stallman set up the Free Software Foundation (FSF). Inthe mid- and late-80s, FSF hired software developers to write thesoftware needed for GNU. At its peak it had 15 people on its staff. FSFalso holds the copyrights for some GNU software packages. Most GNUpackages are licensed under the GNU General Public License (GNU GPL),while a few use the GNU Lesser General Public License (GNU LGPL), and astill smaller amount use other free software licenses.
　　So that it would be convenient for peopleto switch to GNU, it was decided that GNU would be mostly compatiblewith Unix, which was a popular proprietary operating system at thetime. The design of Unix had proven to be solid, and it was modular, soit could be reimplemented piece by piece.
　　As GNU gained prominence, interestedbusinesses began contributing to development or selling GNU softwareand technical support. The most prominent and successful of these wasCygnus Solutions, now part of Red Hat.
　　Licensing
　　In order to ensure that GNU softwareremains free, the project released the first version of the GNU GeneralPublic License (GNU GPL) in 1989. This license is now used by most GNUprograms, as well as a large number of free software programs that arenot part of the GNU project; it is the most commonly used free softwarelicense in the world. It gives all recipients of a program the right torun, copy, modify and distribute it, while forbidding them fromimposing further restrictions on any copies they distribute. This ideais referred to as copyleft.
　　Design and implementation
　　The initial plan for GNU was to be mostlyUnix-compatible, while adding enhancements where they were useful. Thedesign of the kernel was GNU's largest departure from "traditional"Unix. GNU's kernel was to be a multi-server micro-kernel.
　　The GNU Hurd runs on a microkernel(currently Mach) and consists of a set of programs called servers thatoffers the same functionality as the traditional Unix kernel (or Linux).
　　GNU (using Hurd) can be tried using a live CD. (See External links).
　　By 1990, the GNU system had an extensibletext editor (Emacs), a very successful optimizing compiler (GCC), andmost of the core libraries and utilities of a standard Unixdistribution. The main component still missing was the kernel. In theGNU Manifesto, Stallman had mentioned that "an initial kernel existsbut many more features are needed to emulate Unix." He was referring toTRIX, a remote procedure call kernel developed at MIT, whose authorshad decided to distribute for free, and was compatible with Version 7Unix. In December 1986, work had started on modifying this kernel.However, the developers eventually decided it was unusable as astarting point, primarily because it only ran on "an obscure, expensive68000 box" and would therefore have to be ported to other architecturesbefore it could be used. By 1988, the Mach message-passing kernel beingdeveloped at Carnegie Mellon University was being considered instead,although its release as free software was delayed till 1990 while itsdevelopers worked to remove code owned by AT&T.
　　Since the Mach microkernel, by design,provided just the low-level kernel functionality, the GNU Project hadto develop the higher-level parts of the kernel, as a collection ofuser programs. Initially, this collection was to be called Alix, butdeveloper Michael Bushnell later preferred the name Hurd, so the Alixname was moved to a subsystem and eventually dropped completely.Eventually, development of the Hurd stalled due to technical reasonsand personality conflicts.
　　GNU/Hurd refers to the GNU OS distributionthat uses GNU Hurd as its core. GNU Hurd is the set of programs orservers run on top of a microkernel (it currently uses the GNU Machmicrokernel, but efforts port the Hurd to the L4 microkernel arecurrently ongoing). The "GNU" in GNU Hurd indicates that it is a partof the GNU project, while "GNU/Hurd" distinguishes it as one of the twocurrently available GNU systems, that is, Linux-based GNU systems (or"GNU/Linux") as opposed to Hurd-based GNU systems (or "GNU/Hurd"). Just"GNU" refers to GNU/Hurd or a Hurd-based GNU system. "GNU/Linux" ispronounced "GNU-slash-Linux", or more often, just "GNU Linux". However,the FSF contests that "GNU Linux", by the rules of the Englishlanguage, refers to a distribution of the kernel Linux by the GNUproject or GNU project's version of it; "GNU/Linux", they say, makes itclear that a person is referring to the combination of the kernel Linuxand the GNU userland binaries, forming a complete GNU OS. LinusTorvalds, original author of the kernel, does not approve of the term"GNU/Linux"; he prefers "GNU Linux" if the GNU project "wants its owndistribution."
　　In 1991, Linus Torvalds wrote theUnix-compatible Linux kernel. Although it was not originally freesoftware, Torvalds changed the license to the GNU GPL in 1992. Linuxwas further developed by various programmers over the Internet. In1992, it was combined with the GNU system, resulting in a fullyfunctional free operating system. The GNU system is most commonlyencountered in this form, usually referred to as a "GNU/Linux system"or a "Linux distribution". As of 2005, Hurd is in slow development, andis now the official kernel of the GNU system. There is also a projectworking on porting the GNU system to the kernels of FreeBSD and NetBSD.
　　On the 20th anniversary of the GNU Project(January 5, 2004), the Irish Free Software Organisation was founded topromote free software in Ireland.
　　GNU software
　　Prominent components of the GNU systeminclude the GNU Compiler Collection (GCC), the GNU C Library (glibc),the GNU Emacs text editor, and the GNOME graphical desktop.
　　Many GNU programs have been ported to otheroperating systems and are often installed on proprietary UNIX systemsto replace the proprietary utilities. As well as giving users freedom,many of these GNU programs have been proven to be more reliable thantheir proprietary Unix counterparts [2]. The reputation of GNU softwareis especially good for its software development tools, which aresometimes collectively called the GNU toolset. Making up but a smallfraction of the GNU system as a whole, some people consider the toolsetto be of superior quality to many of the equivalent Unix versions, evenif the GNU versions are not totally POSIX compliant. With thepopularity of GNU/Linux systems, many developers install the GNUtoolset on other systems for compatibility or to capture uniformbehavior across platforms. Many GNU programs have also been ported toMicrosoft Windows, Mac OS X, and various other proprietary platforms,however, the motive for developing these programs was to contribute toreplacing those systems with free software, not to enhance them.