For those who don't know "forking" is creating a new version of some open source project. But it's important to know also that this term is just a phrase or idiom which is something open source developers say when they don't want to listen to user feedback.
Forking is in theory possible, but it almost never works. Most of the open source projects are linux-based and this is actually a big obstacle for Windows developers. Often the problem is not in the main source code itself, but in required libraries which in worst case require compiling from the source. To remain sane it's best to be a linux user, but the irony is that only crazy people use linux. Those who think the government is watching them when they wrap their joyrod in tin foil while watching Alanah Pearce's cosplay videos for research purposes.
The second problem is that most open source projects are large. It's not easy to fork them just like that. You need to know how to program in the first place and then how to use some of the usual libraries like wxWidgets or whatever in the context of the project. The overall quality and structure of open source projects is poor, sometimes very bad, so it makes forking even harder when the source code is not that readable.
These two problems are the main reasons why we don't see forks. If it were easy we would see forks with projects like GIMP which is slow, buggy and badly designed. You wish someone would fix it, but nothing ever happens.
So why don't the developers listen to feedback and fix their projects? It's an interesting question which calls for wearing tin foil in whatever bodypart you want to. We do have many open source projects which are almost as good as commercial software, but never better. Big projects are run by foundations or similar quite shady groups of people and money is involved in the development in one way or another. Sometimes it feels like "they" don't want to make software better than commercial versions.
Forking is a smoke screen, it's a way to end the conversation about how to fix the project. I believe all bigger open source projects are monitored by people who don't want free alternatives to replace commercial software. They watch these projects and start to ruin them when they become too good. Just look at what happened to Blender 3D. They made the UI much worse and we still have to fight against that ridiculous right button select issue. Blender is run by a strange millionaire who is taking orders from no one, well other than his illuminati friends I guess.
Another strange thing indeed is that most of these so called free open source developers are millionaires. How did they get their money? Even Linus "Rolle" Torvalds is a multi-millionaire and he did what? He took some ancient unix source code and forked it to a new operating system. Where did his money come from? Who paid him to create an operating system which would never be a viable option for commercial systems, but would rather confuse everyone for empty promises.
I think the whole open source ideology was ruined by "them", the people who did not want it to succeed over commercial software. Let's hope that some day we will learn the truth and begin a new era of open source development.