The Reelay project is licensed under the MPL 2.0.
The MPL 2.0 is a simple copyleft license. The MPL's "file-level" copyleft is designed to encourage contributors to share modifications they make to your code, while still allowing them to combine your code with code under other licenses (open or proprietary) with minimal restrictions.
Please also check frequently asked questions and answers about using and distributing code under the MPL 2.0 from here.