EDIT: I'm fascinated by the childishness of those who are complaining about the $10. Not only you don't have to pay it, and not only that it's open source, and not only the intentions are clear on why it's not a permissive license made to fight filling average Joe with malware like always being done with NewPipe and others on Play Store, but also you can pick your poison. Would you like google to win this dumb war on ad blockers? Or would you like to support non-perfect people making FOSS apps for your benefit? I really don't get you, guys. Pick your battles! Take the win and shut up for once!
I see there's a lot of negativity around GrayJay and their licensing and I don't disagree; but there's a battle going on here It's Google against the world. Having private paid entities working on this alongside the FOSS efforts is definitely not a bad thing. The fact that they're running source available means that other people can look at what they're doing even if they can't use their code directly.
Yeah ultimately the OSS is more important to me than the F. I want FOSS ultimately but the former is massive step up from the status quo and, frankly, a more reasonable goal in my lifetime.
They can use the code directly. The license allows "review, compilation and non-commercial distribution".
It doesn't explicitly allow modification, but they do define "code" as "the code and any part of it and any derivative of it", so clearly derivatives are expected.
However, almost all these guys are using the same libraries under the hood. When Google breaks one you're probably going to break most of them leaving us all scrambling to find the next way.