Linus Torvalds [off-list ref] writes:
Think of something like a collection of projects, each under their own
subdirectory. We could eventually literally make them _look_ like one big
project, with cross-project commits grafted together, but they'd
technically be totally independent (think "git" vs "gitk" - rather than
having a very tight merge like I did, we could have tried to make it be a
more virtual graft instead).
One posibility for a collection of projects is to make them with a tree of
commits instead of a tree of trees and blobs.
Santi