> Then you're doing federated development, and you should continue to use Git or another tool that supports that style of development as a first-class activity.

So, let's say I want to work on an open source project done in fossil. Let's say I don't personally know anyone associated with the project, and kind of just want to play around with it and I'm not even sure I'll be able to fix any bugs or add any useful features, or I just want to hack on an idea I had. How do I do this? Private branches? Isn't that what git offers?

Sure, if there is never an expectation of an outsider looking at or hacking on the code, then a non-federated tool might make sense, but in any situation where the code is suppose to be public, I don't understand where the advantage is (or why I would ever voluntarily learn fossil unless as employer required it).