Dual Licensing

ZK follows the dual licensing model used by MySQL, Sleepycat, and other companies. The dual licensing model is based on the principle of fair exchange or Quid pro Quo ("something for something"). The dual licensing model offers you a choice of either an open source license or a commercial license. This model is becoming common as a sustainable way to support open source development over time.

From licensing perspective, we have two different products depending on usage and distribution, though technically they have the same source code. ZK's dual licensing options include:

• The ZK Open Source License allows you to offer your software under an open source/ freeware license (GPL) to allow all who wish to use, modify, and distribute it freely. The Open Source License allows you to use the software at no charge under the condition that if you use ZK code in an application you redistribute, the complete source code for your application must be available and freely redistributable under reasonable conditions. ZK bases interpretation of the GPL on the Free Software Foundation's Frequently Asked Questions.
• The ZK Commercial License, which allows you to provide commercial software license to your customer or distribute ZK-based application. This is for organizations that do not want to release the source code for their applications as open source / freeware; in other words, they do not want to comply with the GPL. For more detail on the Commercial non-GPL License, click here. Or, if you want more information on pricing, click here.

Today the GNU GPL is the most widely used free software license. According to eWeek, Eben Moglen, General Counsel for the FSF estimates that 65 percent to 70 percent of all open-source projects are licensed under the GPL. We believe in open source software. We believe it is the most effective way to develop, at least, software frameworks. We welcome all initiatives to publish more software under the GPL license, just as we have done.

In their simplest form, the following are general licensing guidelines:

• If your software is licensed under either the GPL-compatible Free Software License as defined by the Free Software Foundation or approved by OSI, then use our GPL licensed version.
• If you distribute a proprietary application in any way, and you are not licensing and distributing your source code under GPL, you need to purchase a commercial license of ZK.
• If you are unsure, we recommend that you buy our cost effective commercial licenses. That is the safest solution. For licensing questions, we encourage you to refer to the Free Software Foundation or a lawyer as appropriate.

Commercially licensed customers get commercially supported product with assurances from Potix Corporation. Commercially licensed users are also free from the requirement of making their own application open source.

For OEM's, ISVs, corporate, and government users, a commercial license is the proper solution because it provides you with assurance from the vendor and releases you from the strict requirements of GPL license.

Nevertheless, you can download, inspect, and test ZK code under the GPL licenses before you purchase a commercial non-GPL license.