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'Dual-licensing' is the practice of distributing identical software under two different sets of terms and conditions. This may mean two different licences, or two different sets of licences. Software is sometimes offered under more than two licences, in which cases 'tri-licensing' or 'multi-licensing' may be a more accurate term.
When software is dual-licensed, recipients can choose which terms they want to use or distribute the software under. The distributor may or may not apply a fee to either option.
The two usual motivations for dual-licensing are licence compatibility and market segregation based business models.

Contents

Business models

Licence compatibility

Market segregation in proprietary software

External links

Business models

This is commonly done to support free software business models. In this model, one option is a proprietary software licence, which allows the possibility of creating proprietary applications derived from it, while the other licence is a copyleft free software/open source licence, thus requiring any derived work to be released under the same licence. The copyright holder of the software then typically gives away the free/open source version of the software at no cost, and profits by selling licenses to commercial operations looking to incorporate the software into their own business.
Since in most cases only the copyright holder can change the licensing terms of a software, dual licensing is mostly used by companies that wholly own the software which they are licensing.
Dual licensing is used by the copyright holders of some free software packages advertising their willingness to distribute using both a copyleft free software licence and a non-free software licence. The latter licence typically offers users the software as proprietary software or offers third parties the source code without copyleft provisions. Copyright holders are exercising the monopoly they're provided under copyright in this scenario, but also use dual licensing to discriminate the rights and freedoms different recipients receive.
Such licensing allows the holder to offer customisations, early releases, generate other derivative works or grant rights to third parties to redistribute proprietary versions all while offering everyone a free version of the software. Sharing the package as copyleft free software can benefit the copyright holder by receiving contributions from users and hackers of the free software community. These contributions can be the support of a dedicated user community, word of mouth marketing or modifications that are made available as stipulated by a copyleft licence. However, a copyright holder's commitment to elude copyleft provisions and advertise proprietary redistributions risks losing confidence and support from free software users. [1] [2]
Examples include MySQL AB's database, Gaia Ajax Widgets, and TrollTech's Qt development toolkit.

Licence compatibility

A second use of dual-licensing with free software is for licence compatibility, allowing code from differently licensed free software projects to be combined, or to provide users the preference to pick a licence.
Examples include Mozilla Application Suite, which is tri-licensed GPL/LGPL/MPL, Perl which is dual licensed GPL/Artistic License, and OpenOffice.org which is a mixture of GPL/CDDL and GPL/LGPL/CDDL.

Market segregation in proprietary software

Dual licensing is also used by some distributors of non-free software. Sometimes this is done to proprietary software to segregate a market. By splitting people into multiple categories such as home users, professional users, and academic users, copyright holders can set different prices for each group. However, among proprietary software, it is more common "home edition" and "professional edition" be also differentiated by the software included, not just the licence.

External links

★ Dual Licensing information from 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