Licensing Policy

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.

VoIP developers may license our Zfone libZRTP Software Development Kit (SDK) to add Zfone's ZRTP protocol to their VoIP applications. The Zfone libZRTP SDK is offered under two different licenses: a commercial license for commercial developers, and the GNU GPL version 2 license for open-source developers. Here's how this dual-licensing model works.

For Open Source Projects:

If you are developing and distributing open source applications under the GPL License, then you are free to use the Zfone libZRTP SDK libraries under the GPL License, version 2. The formal terms of the GPL license can be found embedded in the source code file zrtp_legal.c in the Zfone libZRTP SDK source distribution package. Any software that uses code under a GPL license is itself subject to the same GPL licensing terms. For licensing the Zfone libZRTP SDK under alternate terms, so that you can use it without your own product becoming infected with the obligations of the GPL, you should contact us to purchase a commercial license.

If you need the Zfone SDK for other non-GPL open source applications, contact us. We can probably work something out to meet your open source licensing needs on a case-by-case basis.

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 copyright 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 to integrate into their products. The rest of the Zfone software is not needed if you just want to add the ZRTP protocol to your VoIP application.

If you license the Zfone SDK under the GPL, you do not need a separate signed agreement with Zfone, because the GPL license is sufficient. We do, however, recommend you contact us to ensure interoperability of your products with other ZRTP-based products such as ours. Also, there may be opportunities for partnerships and co-marketing.

Under the GPL, you must release the complete source code for the application that is built on the Zfone SDK. You do not need to release the source code for components that are generally installed on the operating system on which your application runs, such as system header files or libraries.

Free use for those who never copy, modify or distribute. As long as you never distribute the Zfone SDK Software in any way, you are free to use it in your application, irrespective of whether your application is under GPL license or not.

If you create a derivative work from the Zfone SDK source code, and wish to distribute it to others, it must be licensed under the GPL as well.

You are allowed to copy Zfone SDK binaries and source code, but when you do so, the copies will fall under the GPL license.

For Commercial developers who distribute the Zfone SDK with their products, and do not license and distribute their source code under the GPL, Zfone provides a flexible commercial license.

When in Doubt

If you're not sure which license applies to you, or you have any questions about licensing, please contact us to explore the options available for your specific scenario. Keep this principle in mind: If our software makes money for you, we deserve to be paid something too. Hence, our commercial license.

For Commercial Projects:

The Commercial License is an agreement with Zfone for organizations that do not want to release their application source code. Commercially licensed customers get a commercially supported product with assurances from Zfone. Commercially licensed users are also free from the requirement of making their own application open source.

Typical examples of Zfone distribution include:

Selling software that includes Zfone SDK software to customers who install the software on their own machines;
Selling software that requires customers to install the Zfone SDK on their own machines; or
Building a hardware system (such as a phone or a PBX, for example) that includes the Zfone SDK and selling that hardware system to customers for installation at their own locations.

Specifically:

If you include the Zfone SDK with an application that is not licensed under the GPL or GPL-compatible license, you need a commercial license for the Zfone SDK.
If you develop and distribute a commercial application and as part of utilizing your application, the end-user must download a copy of Zfone or the Zfone SDK; for each derivative work, you (or, in some cases, your end-user) need a commercial license for the Zfone SDK libraries.

GPL users have no direct legal relationship with Zfone. The commercial license, on the other hand, is Zfone's private license, and provides a direct legal relationship with Zfone.

Recommendations

To all commercial and government organizations, we recommend the commercial license. This frees you from the broad and strict requirements of the GPL license.
To all free software enthusiasts we recommend the GPL license.
To anyone in doubt, we recommend the commercial license.

Frequently Asked Questions about our licensing policy

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 copyright status of those components remains proprietary.

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. If our software makes money for you, we feel we deserve to be paid too. 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: Is the Zfone application available under the GPL?

A: No. Zfone is a complete software application for end users that showcases the libZRTP SDK. Our libZRTP SDK is a subroutine library for developers that implements the ZRTP protocol, and is available under the GPL. But the rest of the Zfone application, which is not part of the libZRTP SDK, is not licensed under the GPL or any other open source license.

Q: Why does Zfone offer two licenses?

A: Zfone's dual license model supports our 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. If our software makes money for you, we feel we deserve to be paid too.

So if you use the Zfone libZRTP 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?