noch alpha: 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.
Camlistore is: a way to store, sync, share, model and back up content a work in progress Open Source (Apache licensed)
CouchDB hosting in the cloud. Up to 1GB free. [currently invite only, private beta]
Simple ruby script to archive a rss feed to a SQL backend