As Lightning Dart is based on the Salesforce Lightning Design System (SLDS), it inherits the licenses.
- SCSS - BSD License Clause 2
- Icons, Images - Creative Commons Attribution-NoDerivatives 4.0
- Fonts - Font License
Please check the SLDS site for details.
The Lightning Dart code (functionality and SCSS extensions) itself is licensed via GPL 3.0
For a small, nominal fee, we will you provide you a commercial license, just create a ticket or send an email to email@example.com.