Cooki3d use the Dual Licensing.

The Dual Licensing business model allows software companies to provide their products for two distinct uses - commercial and open source software development.

It is the same model than QT4 Business Model

As a general rule:

• If you wish to derive a commercial advantage by not releasing your application under an open source license, you must purchase an appropriate number of commercial licenses from Cooki3d. By purchasing commercial licenses, you are no longer obligated to publish your source code.
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• If you wish to use an open source version of Cooki3d's products, you must contribute all your source code to the open source community at large, according to the terms of the applicable open source license. In this case, the Cooki3d part is released under the GNU/GPL License