Não tenho certeza se ele fará o que você quer, mas dê uma olhada em ZendTo
This is a web-based package that will let you provide a secure and easy-to-use method for your users to be able to exchange files with other people, even with people on other sites that do not have any login rights at your site.
Unlike other commercial services, you do not have to trust your files or login rights to any other services; you run all of it yourself. It integrates with your existing authentication system if you have one, or else it can use its own secure SQL-based user authentication system. It will integrate with any Active Directory, LDAP or IMAP system you already have in place.
It was originally based on the "Dropbox" package written by the University of Delaware.