軟件分類：自由軟件、開放源代碼軟件、公共軟件、私有軟件、版權所無軟件

自由軟件（free software）

"Free software" means software that respects users' freedom and community. Roughly, it means that the users have the freedom to run, copy, distribute, study, change and improve the software. Thus, "free software" is a matter of liberty, not price ^[1].

 

"Free software" gives users access to source code. Users have the rights to use the software, redistribute it, modify it, and distribute their modifications. Users can receive payment for these distributions. However, since any user can redistribute as many copies of the software as they would like, the price is normally very close to the cost of media. Other than the copylefted^* conditions below there are virtually no restrictions on the use of the software or how it can be modified. This includes primarily public domain software and copylefted software^[2].

自由軟件關注的重點在於用戶對軟件的絕對支配權，能夠自由地運行、複製、散佈、學習、修改並改進該軟件，而不在於軟件是免費與否。若是一個軟件爲自由軟件，那麼它須要提供如下四種自由度^[1]：

Freedom 0: The freedom to run the program as you wish, for any purpose. 不管何種目的，用戶能夠自由地運行該軟件。

 

Freedom 1: The freedom to study how the program works, and change it so it does your computing as you wish. Access to the source code is a precondition for this. 用戶能夠自由地學習並修改該軟件用於實現用戶想獲得的計算。前提是用戶獲得軟件的源代碼。

 

Freedom 2: The freedom to redistribute copies so you can help others. 用戶能夠自由地散佈該軟件的複製用於幫助別人。

 

Freedom 3: The freedom to distribute copies of your modified versions to others. By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precodition for this. 用戶能夠自由地散佈該軟件修改後的複製，所以整個社區均可以得益於修改後的軟件。前提是用於獲得軟件的源代碼。    

可見，訪問軟件源代碼是其成爲自由軟件的必要條件。用戶能夠自由地修改軟件並散佈給其餘人而不須要任何許可。一般自由軟件都比非自由軟件更加可靠。

 

開放源代碼軟件（open source software）

"Open source software" is used by some people to mean more or less the same category as free software. It is not exactly the same class of software: they accept some licenses that we consider too restrictive, and there are free software licenses they have not accepted. However, the differences in extension of the category are small: we know of only a few cases of source code that is open source but not free. In principle it could happen that some free programs are rejected as open source, but we don't know if that has ever happened^[3]. 

開放源代碼軟件與自由軟件的含義有些相似，所以也常常被混淆。可是從上面能夠看出，開放源代碼軟件只是自由軟件的一部分，並不能徹底替代自由軟件。開發者更傾向於使用「自由軟件」的概念。

 

 公共軟件（public domain software）

"Public domain software" is source code that has no restrictions on use or distribution. It can be used in any way, copied, modified, distributed, and sold with any added licensing terms desired^[2].

 

"Public domain software" is software that is not copyrighted. If the source code is in the public domain, that is a special case of non-copylefted free software, which means that some copies or modified versions may not be free at all^[3].

 公共軟件沒有版權，所以修改後的軟件被添加了一些許可後就再也不是自由的了。所以能夠說公共軟件不是copylefted的。

 

私有軟件（proprietary software）

「Proprietary software」 is the traditional commercial model. Software executables are sold or leased with no user right to distribute the executable to others. Commercial licensing terms very, but limited copying rights may apply for backups or for other fair uses that do not deprive the software vendor from rightful income under its license. Source code is not provided under this model[2].

私有軟件不提供源代碼，用戶也沒有散佈、複製、修改的權利。

 

共享軟件（shareware）

 Shareware executables have no restrictions on distribution, but users are required to pay for the software under the honor system if they decide to use it. Source code is not provided^[2].

 

Shareware is software which comes with permission for people to redistribute copies, but says that anyone who continues to use a copy is required to pay a license fee^[3]. 

 共享軟件不限制軟件的散佈，可是不提供源代碼，想要使用該軟件須要支付費用。所以共享軟件並非自由軟件。

 

版權所無軟件（copylefted software）

"Copylefted software" is free software that has been copyrighted so that the users rights modify and redistribute the source code are always transferred to subsequent users^[2]. 

 

"Copylefted software" is free software whose distribution terms ensure that all copies of all versions carry more or less the same distribution terms^[3].

 版權所無軟件是一種自由軟件，用戶修改後的軟件在散佈時要遵照原始軟件的條款和許可。GNU發佈的General Public License (GPL)是一個特定的版權所無許可，用以保證自由軟件對全部用戶是自由的。

 

 Reference

[1].https://www.gnu.org/philosophy/free-sw.en.html

[2].Shackleford W P, Proctor F M. Use of open source distribution for a machine tool controller[C]//Sensors and Controls for Intelligent Manufacturing. International Society for Optics and Photonics, 2001, 4191: 19-30.

[3].https://www.gnu.org/philosophy/categories.en.html

*Copyleft 著佐權，是一個由自由軟件運動所發展的概念，是一種利用現有著做權體制來保護全部用戶和二次開發者的自由的受權方式。在自由軟件受權方式中增長著佐權條款後，該自由軟件除了容許使用者自由使用、散步、修改以外，著佐權許可證更要求使用者修改後的衍生做品必需要以同等的受權方式釋出以回饋社會。——百度百科