多重許可

多重许可是一种在不同的许可证下发布同一个软件的方式。软件发行方通常采用两个或以上的许可证，或许可集。

当一个软件采用多重许可时，接收者可以选择他们愿意遵守的许可发布衍生品。但软件包或库中存在多个许可证并不意味着接受者可以任选其一。在某些情况下，例如如软件包中有多个以不同许可证发布的软件，则接收者必须遵守所有许可证的条款。多重许可两个常见用途是解决许可证兼容性^[1]和开源软件商业化。^[2]

商业模式

对于商业公司而言，多重许可通常用于支持自由软件的商业化。这种情况下，软件会采用两种许可：专有软件许可证（允许创建专有应用程序）和Copyleft 自由软件/开源许可证，软件通常以极低的价格或免费提供社区版本，并通过向商业机构出售专有许可证来获利。这种模式与共享软件相似。

自由软件公司可以使用多重许可来提供不同的服务。例如，可以为企业级用户提供个性化服务、提前发布稳定版、授予发布专有作品的权利，同时向所有人提供开源的免费版。这样，软件可以受到来自开源社区用户、黑客的贡献，这些贡献可以是修改源码、提升口碑、对专有许可用户的支持等。但是，若不尊重开源社区的贡献，如在许可证中增设不平等条款^[4]、涉嫌窃取开源社区成果^[5]等，则可能失去支持。

采用多重许可的软件包括NetBeans IDE 、MySQL、 Asterisk 、Berkeley DB 、 Modelio 、Ice 、 Magnolia CMS 、 JUCE 、 wolfSSL ^[6]和Qt开发工具包等。

多重许可的一个典型例子是MySQL。Oracle MySQL 有多个版本，MySQL 企业版^[7]、MySQL 标准版、MySQL Cluster 运营商级版需要付费，以每月订阅形式提供许可。其他版本，如 MySQL 经典版、MySQL 社区版等，则可以免费使用，但有一些限制（采用GPL协议、仅提供社区支持等）。 ^[8]

许可证兼容性

多重许可可以保证许可证兼容性 ^[1]，即允许用户选择不同许可证，合并不同自由软件的源码，绕过许可证冲突问题。

举例：

Mozilla早期开发的软件，如Mozilla应用套件、早期的Firefox和Thunderbird等，均采用三重许可分发源码，分别为Mozilla公共许可证（MPL）1.1、GNU通用公共许可证（GPL）2.0和GNU宽通用公共许可证（LGPL）2.1^[9]。后续MPL 2.1修改了部分条款，使之与GPL兼容，不再需要使用三重许可。^[10]
Perl采用GPL、艺术许可协议双重许可。^[11]
Ruby的许可证明确包含了对GPL的双重许可。

参考来源

^ ^1.0 ^1.1 Nikolai Bezroukov. Comparative merits of GPL, BSD and Artistic licences (Critique of Viral Nature of GPL v.2 - or In Defense of Dual Licensing Idea). 2001. （原始内容存档于2001-12-22）. Viral property stimulates proliferation of licenses and contributes to the "GPL-enforced nightmare" -- a situation when many other licenses are logically incompatible with the GPL and make life unnecessary difficult for developers working in the Linux environment (KDE is a good example here, Python is a less known example).
^ Licensing in a Post Copyright World. 2013-07-23. The AGPLv3 was a terrible success, especially among the startup community that found the perfect base license to make dual licensing with a commercial license feasible. MongoDB, RethinkDB, OpenERP, SugarCRM as well as WURFL all now utilize the AGPLv3 as a vehicle for dual commercial licensing. The AGPLv3 makes that generally easy to accomplish as the original copyright author has the rights to make a commercial license possible but nobody who receives the sourcecode itself through the APLv3 inherits that right. I am not sure if that was the intended use of the license, but that's at least what it's definitely being used for now.
^ Digium Incorporated. Asterisk Guidelines, The contributor license agreement. [2009-02-10].
^ 关于 Netscape 公共许可证. GNU.
^ 苹果许可证（APSL）1.1版本的问题.
^ wolfSSL Embedded SSL/TLS Library | Now Supporting TLS 1.3. [2020-01-27] （美国英语）.
^ My SQL Enterprise Edition. Oracle. [25 April 2013].
^ MySQL Community Edition. Oracle, MySQL. [25 April 2013].
^ Mozilla Foundation. Mozilla Code Licensing. [2007-09-17].
^ MPL 2 Upgrade. [2012-08-18].
^ The Perl Foundation. Perl Licensing - perl.org. [2007-09-17].

外部链接

Dual Licensing information from OSS Watch（英语：OSS Watch）
Article "Does dual licensing threaten free software?" by Glyn Moody
Article "The Dual-Licensing Model" by Don Marti
Article "Dual Licensing: Having Your Cake and Eating It Too" by Philip H. Albert
Article "Dual-Licensing Open Source Business Models" by Heather Meeker
Article "How to use open source as a power marketing tool" by John Koenig
Paper "Dual Licensing in Open Source Software Industry" by Mikko Välimäki
Dual Licensing Schemes
"Should code be “dual licensed” under the GPL and a permissive license?" by Software Freedom Law Center
Combining GPL, closed code. [2013-01-03]. （原始内容存档于2013-01-03）.

这是一篇與软件相關的小作品。您可以通过编辑或修订扩充其内容。

[GPLviral-1] 1.0 ^1.1 Nikolai Bezroukov. Comparative merits of GPL, BSD and Artistic licences (Critique of Viral Nature of GPL v.2 - or In Defense of Dual Licensing Idea). 2001. （原始内容存档于2001-12-22）. Viral property stimulates proliferation of licenses and contributes to the "GPL-enforced nightmare" -- a situation when many other licenses are logically incompatible with the GPL and make life unnecessary difficult for developers working in the Linux environment (KDE is a good example here, Python is a less known example).

[2] Licensing in a Post Copyright World. 2013-07-23. The AGPLv3 was a terrible success, especially among the startup community that found the perfect base license to make dual licensing with a commercial license feasible. MongoDB, RethinkDB, OpenERP, SugarCRM as well as WURFL all now utilize the AGPLv3 as a vehicle for dual commercial licensing. The AGPLv3 makes that generally easy to accomplish as the original copyright author has the rights to make a commercial license possible but nobody who receives the sourcecode itself through the APLv3 inherits that right. I am not sure if that was the intended use of the license, but that's at least what it's definitely being used for now.

[3] Digium Incorporated. Asterisk Guidelines, The contributor license agreement. [2009-02-10].

[4] 关于 Netscape 公共许可证. GNU.

[5] 苹果许可证（APSL）1.1版本的问题.

[6] wolfSSL Embedded SSL/TLS Library | Now Supporting TLS 1.3. [2020-01-27] （美国英语）.

[7] My SQL Enterprise Edition. Oracle. [25 April 2013].

[8] MySQL Community Edition. Oracle, MySQL. [25 April 2013].

[9] Mozilla Foundation. Mozilla Code Licensing. [2007-09-17].

[10] MPL 2 Upgrade. [2012-08-18].

[11] The Perl Foundation. Perl Licensing - perl.org. [2007-09-17].

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