I don't know anything about dropbox, but based on the types of things the author spends time thinking about, I think s/he might find http://git-annex.branchable

I don't know anything about dropbox, but based on the types of things the author spends time thinking about, I think s/he might find http://git-annex.branchable.com/assistant/ http://git-annex.branchable.com/assistant/ useful.