Syncany - Open source Dropbox variant uses independent storage
Syncany is an open-source cloud storage and filesharing application. It allows users to backup and share certain folders of their workstations using any kind of storage, e.g. FTP, Amazon S3 or Google Storage. While the basic idea is similar to Dropbox and JungleDisk, Syncany is open-source and additionally provides data encryption and more flexibility in terms of storage type and provider.
Encryption happens locally, so you can store your stuff pretty much anywhere.
I can see this being really useful for a group of friends collaborating on a project or a small business that would like Dropbox-ish convenience without relying on a third party.
That said, it’s very new, unstable and currently available for Linux only—one to keep an eye on, though.