There are many cloud file storage services like Dropbox, Google Drive, Box.net each offering some space. Drive Stack intends to stack up all these drives to create a drive stack. Drive Stack is just like another disk , upload files to it , download files from it making it easy to use application for managing your cloud storage.
Drive Stack has many inbuilt routing and optimizations so that you can have files larger than any of your individual disks be uploaded by sharding, choosing the drive to upload your file to based on available space, etc.
The app is well far from production but you could give it a test drive at : http://www.hackyourworld.org/~iitb_ashwin/