You can fork it but you can’t redistribute it or change the name. You also can’t do anything that would be considered making a profit.
Essentially you can’t do anything but contribute free labor. If Greyjay put ads and malware into the app you would be powerless to start something based on it.
The source is available, right? You just can’t fork it to include ads? Or you can’t fork it at all?
You can fork it but you can’t redistribute it or change the name. You also can’t do anything that would be considered making a profit.
Essentially you can’t do anything but contribute free labor. If Greyjay put ads and malware into the app you would be powerless to start something based on it.