I am in pretty much the same position as the author of this post. I understand my post is something of a duplicate but the link is a few years old and I wonder if the situation has changed any?
I have a client who runs (and loves) a WordPress website and uses Dropbox for sharing files with their clients (typically digital copies of contracts & machine manuals). They don't like using Dropbox as its not integrated with the website and isn't branded. I had hoped there was a Dropbox API that allowed for user/group based access to folders but there doesn't seem to be.
Are there any plugins/services out there that fit the bill or is the only option still to use Amazon S3?