For almost all files, source code is licensed under Apache Software License 2.0.
However, NRF24L01P device support files are licensed under GNU Lesser General Public License 2.1 as derivative work from Cosa library, adapted to fit FastArduino framework.
As a result, any project using FastArduino but not any NRF24L01P stuff, must comply to ASL 2.0: but a project using FastArduino and its NRF24L01P support classes hast to comply to the more restricted LGPL 2.1.
This is also valid for examples accompanying the FastArduino project.