Cafu is available under two licenses:
The source code is in both cases exactly the same, and it depends on your goals and requirements which of the two licenses is the most suitable for you.
Cafu is available to everyone as 100 percent free software under the GNU General Public License (GPL).
If your software is 100 percent free software under the GPL as well, then you never have to pay us for the licenses. (In all other instances, you are better served by our commercial license.)
Please refer to the official GNU GPL website for a detailed explanation of the rights that the GPL grants you and the (very few) obligations that it can impose on you. There you also find the definition of free software, answers to frequently asked questions, and many other pieces of worthwhile information about the GPL.
The one thing that is not possible with Cafu under the GPL is combining it with proprietary (non-free) code and distributing the result publicly. (Non-public use such as private or company internal use is ok, so that you can evaluate and test Cafu to your heart's content.)
That is, you can not use the free Cafu source code in order to create a new program (e.g. a computer game) that is publicly distributed without releasing the full source code (including all of your previously closed, proprietary parts) under the GPL as well. Please consult the GPL text and the GPL FAQs for details.
The solution is to get Cafu directly from CFS under a custom license that is tailored to your needs:
In summary, just let us know that you want a custom license, and what you want the license to look like. Mention any detail that is important to you. We're looking forward to work out the details together with you!
All external libraries that are used in Cafu are legally compatible with closed-source use, and none of them imposes GPL-like restrictions of its own. See file LICENSE.txt for details, or ask us if you have any questions!