I'm far from an expert on this, so other commenters please correct me if I'm wrong: GPL requires that any project that uses a GPL project as a part of it must

I'm far from an expert on this, so other commenters please correct me if I'm wrong: GPL requires that any project that uses a GPL project as a part of it must also be free and open source. It looks like Parity requires that you pay a licensing fee to the original creator of the Parity licensed project if you're using it for non-open-source reasons. So, it can be used for private/for-profit projects, but you have to pay for it in that case, whereas open source projects can use the code for free.