Quicksand Automatically Syncs Your Recent Files to the Cloud
Quicksand is a magical little mac app that lets you forget about having to upload or sync files into the cloud. Every time you open a file, quicksand will automatically move it into your cloud folder (dropbox, Google Drive, Copy etc.). So know you don't need to worry about moving things manually - you'll always have access to your most recent files.
Through the settings you can customise what files it should ignore (or only transfer), and set a maximum number of files or diskspace.