SDF3 is dual licensed. You can choose between the GNU GPL and the SDF3 Proprietary License. The GNU GPL gives you the right to use, modify and redistribute SDF3 under certain conditions. Using SDF3 under the terms of the GNU GPL is free of charge.
The SDF3 Proprietary License gives you the right to use the source code for making your own commercial software. It allows you full protection of your work made with SDF3. The exact terms of this license will be established through a contract between you and the Eindhoven University of Technology. For more information on the SDF3 Proprietary License, please contact us at firstname.lastname@example.org.