I wouldn't put fossil in that list of collaboration, since its not really a collaborative tool, or more like, there are barriers to that collaboration, like creating a username for each fossil repository. That's a huge barrier in my view. It would be nice if there was something like a general auth identity that can be used everywhere but that's still not implemented.

FWIW, mercurial seems to have an advantage over git, and that support for BIG repositories which seems to be provided by facebook of all people, so until facebook moves to git, mercurial lives on.