Recently Matt Mullenweg called out Wix for violating the GPL. Wix's CEO, Avishai Abrahami's post on the company blog missed some of the key issues when it comes to using code licensed under the terms of the GNU General Public License. The GPL doesn't require you to only release the changes made to a dependency. If you use a GPL library in your project, then the entire project is deemed to be a derivate work. This is why the GPL is called a viral license, because if one part of your project is covered by the GPL, then it applies to the entirety of your app. Other people more qualified than me have explained this in more detail, more elegantly than I ever could.
This reminded me of a popular platform that is built on a GPL violation. FlightRadar24 allows users to track flights in real time. FR24's data is collected from multiple sources, including the US FAA and a network of volunteers that run tracking equipment. One of the most common tracking setups uses a Raspberry Pi hooked up to a cheap DVB-T USB tuner. librtlsdr is used to tune the USB stick to the right frequency so it can listen to the tracking signals.
The FlightRadar24 software, FR24Feed, is a single binary that includes a statically linked copy of librtlsdr. On multiple occasions I have asked for a full copy of the source code for the FR24Feed binaries that FlightRadar24 are distributing. They have refused.
FlightRadar are under the mistaken belief that they only have to distribute the source for their modifications to librtlsdr. They have made their patched version of the code available on the FlightRadar24 downloads page. FlightRadar24 say they won't release the source to ensure the quality of their data. I'm sorry, but the GPL doesn't include a clause that excuses you from distributing the source code if you have a bad architecture.
It is disappointing to see FlightRadar24 refusing to comply with the terms of the GPL. I still have everything I need to run a tracking station sitting in a drawer. I'll set up my tracking station once FlightRadar24 release all the full source for FR24Feed.