Plone has always been published under the GPL, and will continue to be so in the future. However, as Plone's code base has become more and more componentized, other projects which for various reasons cannot or do not want to use GPL software are interested in reusing some of our core internal framework components.
With this in mind, the Plone Foundation has adopted a new Framework Components Relicensing Policy, which provides a way for us to enable limited relicensing of selected Plone framework components, without compromising our ongoing commitment to Plone as a GPL product. This policy allows Plone community members and package authors to request that the Plone Foundation board of directors relicense certain types of Plone framework components under the modified BSD license instead of the GPL.
For more information and frequently asked questions, please see the complete Plone Framework Components Relicensing Policy document.