One of the great aspects of DotNetNuke is it’s licensing. Its license is based on the BSD license.

What this means is that the software is free for you to do anything you wish without having to submit any modifications or enhancements. This is really useful compared to the GPL where you would have to submit any changes as you will be developing custom modules for yourself that you would probably not want to share.

From their site:

*** Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

The software is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. In no event shall the authors or copyright holders be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the software. ***