git is so agnostic about all this stuff that you can even merge completely disparate, unrelated repositories (for example, my own primary "job" repository, and the linux kernel) into the same on-disk structure. Of course, doing so is useless because none of the commits from one repo has any relevance to the other. But because the commits are identified by true GUIDs, there are no collisions, and both sets of commits can happily exist in a single repo.

It's of almost zero utility, but it does (for me) heighten the beauty and elegance of the concepts behind git (and even, the actual implementation).