One might try to argue that a name used in software code and distributed under some open source license also gives rights to the name by being source ... but to my knowledge there are no court decisions.
> The name “Audacity” is a registered trademark.
It's a regular trademark - it's been acquired.
The trademark isn't covered by the GPL.
Jason Rohrer ran into this very issue when other developers made their own client for his game, using a variation on the game's name. They didn't respond to him asking that they don't use the name, and eventually he was convinced that trademarking the name is the right tool to project it. The original game client is still open-source (and maybe the server too, dunno).
So if for example I wanted to cross-promote my other products or add a "pro" paid version of some sort, I could do that, and those would end up in the main version most people are downloading.
Not sure about this case, but iirc you can have contributors to a project without them owing "part of the copyright" for the stuff they wrote. You just have to make them assign the copyright to you if they want to include their code in the project (they can always fork if they don't like that, but the original authors still get the copyright to the core project).
Also, and orthogonal, a lot of time there are 1-2-5-10 core devs, and the rest 100s are just some small changes here and there, fixes to the documentation, some plugin contribution, etc. In other words, easily writen out, if it comes to that.