Explaining dual licensing

Many commercial open-source vendors offer their software under a dual-licensing model: an open-source license, such as GPL, and a commercial license. An open-source license requires all organizations that use or sell support for the software to offer free redistribution of and access to source code. They also must freely distribute modifications. On the other hand, a commercial license offers the ability to access and modify source code but lacks the distribution requirements.For example, Compiere distributes the community edition of its enterprise software under GPL Version 2 but offers its professional edition under a commercial license. In both cases, the company provides customers with the application source code. However, with a commercial license, customers aren’t required to redistribute their modifications. “The GPL license stipulates that any extensions added to the base GPL product also become subject to the terms of the GPL — which includes that the developer of the extension is forbidden from restricting the use, copying, modification or redistribution of that software and source code,” said John Cingari, Compiere’s chief marketing officer.“For many customers and partners, providing their proprietary extensions back to the public is not practical,” Cingari said. “The commercial license option is preferred by these organizations because they retain control over their innovations that integrate with Compiere.”Similarly, Alfresco provides a commercial license to customers that purchase a subscription.  “They get all the rights of open source/GPL — view and modify the software — without the obligation of redistributing their derivative works,” said Matt Asay, vice president of business development at Alfresco. “This means they can’t redistribute our code, but we’ve yet to find any that want to.”Such commercial licenses don’t comply with the Open Source Initiative’s open-source definition. Asay said some software companies refer to software offered under the commercial license option as source available.