Can you explain what you mean by fossil being a competitor for github, rather than git? Fossil is a scm with additional features for usage, but (the last I used it, and to my memory) it was just the command line fossil very much like git, and that's how I used it.

What makes it the case that fossil cannot be a competitor to git (or hg), in that they are both a vcs?

edit I haven't had a lot of sleep. What I'm trying to ask, I suppose, is why can't you use fossil just like git and ignore any all-in-one features it provides? (This is not to comment on how good, scalable, fast, correct, or robust it is.)