P3.express was originally released under a Creative Commons Attribution-NonCommercial-ShareAlike license, which meant that it’s free (both libre and gratis), and that every derived work should be free as well. As pointed out to us in some of the comments, this may not be a suitable license because, for example, trainers who prepare training content for their P3.express courses may not want to share their course content with everyone.
As a result, after consulting several experts, we’ve changed the license to Creative Commons Attribution. With this license, users have all the previous rights, but they are not limited to publishing their works with the same license – now they can create non-free content based on P3.express.
Creative Commons licenses are irrevocable, which gives trainers and other people who are interested in creating derived work the peace of mind that their investment will not be lost. The reason we were able to change the license as explained above is that the new license is compatible with the previous one and contains all the previous rights. However, we are no longer allowed to switch back from this license to the old license.