My Synology NAS has a pretty good take on personal cloud storage, after I put a domain and SSL on it (which they make really easy with Lets Encrypt) it's pretty much interchangeable with a bunch of cloud services for music, files, tv/video etc. Primarily open source too, they've really done a slick web interface for linux.

Given we're on the brink of putting an extra terabyte or two into your phone or tablet etc I think cloud storage is really going to boil down to allowing others' access.