I'm looking for online storage that can "corral" many other forms of online storage like FTP, SSH, WebDAV, and commercial services like Google Storage and Dropbox, and to keep these files "in sync". In other words, I'm looking for a cloud storage service that will connect all the various forms of storage I work with or that my clients hand to me (i.e. Dropbox) in one virtual filesystem.
Second to that, I'm looking for something with strong versioning features. And second to that, I'm looking for something with good ability to show a "preview" of most file types within the browser, and to let me write notes and annotations on any file type.
P.S. I'm willing to do some work to set up a software stack on a bare-metal machine that I control in order to achieve the desired functionality if there isn't a commercial service that provides all these features.