Licensing FAQ
 Note: The information on this page regarding open source GPL licensing of the Zfone SDK will not go into effect until we're past the beta test phase, which is coming up Real Soon Now. It does NOT apply to the current release of Zfone (from 31 July 2007), which is NOT GPL-licensed software. |
Q: What is Zfone's software licensing model?
A: Zfone uses a "dual licensing" business model. Under this model, developers may choose to use the Zfone libZRTP SDK libraries under the free software/open source GNU General Public License (commonly known as the "GPL") or under a commercial license.
With the GPL license, the Zfone libZRTP SDK libraries are available free of charge, under certain conditions. Developers may download the SDK software for free and modify, integrate, and distribute it with their own GPL'ed products. However, GPL users must abide by the rules of the GPL, which stipulate that if a Zfone-based application is redistributed, the complete source code for this application must also be open and available for redistribution.
Note that only the libZRTP SDK libraries are provided under the GPL. The parts of Zfone that are not part of the libZRTP SDK libraries are not licensed under the GPL or any other open source license. Even if the source code of those components is published for peer review, the intellectual property status of those components remains proprietary. This should not be a problem for developers who wish to include the ZRTP protocol in their GPL'ed products, because they will likely only need the libZRTP SDK libraries.
Zfone offers a commercial license for organizations that do not want to release the source code for their application. Commercial license customers get a commercially supported product with a level of assurance from Zfone, without the requirement that their Zfone-based software must be "open sourced". Zfone is able to provide a commercial license because it has full ownership of the Zfone code.
Zfone's dual licensing increases freedom in two ways: first, it encourages the growth of free software by licensing the Zfone SDK under the GPL; second, it makes it possible to use our software in situations where the GPL is not applicable.
Q: What do you mean by Dual Licensing?
A: “Dual licensing” means that the same code is released under two different licenses. Zfone’s dual licensing model is based on the principle of fair exchange, “Quid Pro Quo, “something for something.” If you are using the Zfone SDK commercially - that is, for creating proprietary software for sale or use in a commercial setting - you must purchase a commercial license from Zfone. Alternatively, if you wish to write Open Source software you can use the Open Source version of the Zfone SDK, released under the GPL. If you use the Open Source version you must release your application and complete source code under the GPL as well. This model has proven successful for a number of leading companies such as mySQL and Sleepycat.
Q: Why does Zfone offer two licenses?
A: Zfone's dual license model supports the company's mission: to make superior secure VoIP software available and affordable to all, and to make money doing it.
The dual licensing creates a circle that sustains both innovation and growth: Zfone channels the revenue from this viable open source business model back into software development that, in turn, supports Zfone's commercial business.
Zfone's open source community gets superior software for no cost, while Zfone's commercial customers have the option of using reliable, peer reviewed, community tested Zfone software for a relatively low cost.
Q: How do I know which license to use?
A: The overall guiding business principle of Zfone's dual licensing is one of fair exchange or "Quid pro Quo" which means "something for something."
So if you use the Zfone SDK with GPL-licensed software (or a license that is GPL-compatible) we encourage you to use the GPL license. For all other users of Zfone or the Zfone SDK, we recommend that you purchase a Zfone commercial license.
Q: Do I get the same Zfone SDK library under either license?
A: Yes. The Zfone SDK library is essentially identical under either the GPL license or the commercial license.
Q: Are other companies using the dual licensing business model?
A: Yes, the dual licensing business model is becoming increasingly popular among open source companies as it paves the way for long-term financial viability. Other companies that offer dual licensing include MySQL, Digium, OSAF, MandrakeSoft, Sleepycat Software, Technical Pursuit, Trolltech, and others.