Sookasa
Sookasa transparently protects files across the Dropbox cloud and linked mobile devices, while preserving the native Dropbox user experience on Windows, Mac, iOS and Android. Sookasa creates a secure folder (called Sookasa) inside Dropbox and will automatically encrypt any file or subfolder placed inside the Sookasa folder. The Sookasa folder will look and feel like a normal folder as long as the user is authorized to access the files. Sookasa allows users to collaborate using the normal Dropbox shared folders interface, and also allows users to securely deliver files to colleagues that do not have Sookasa installed. Sookasa is free for individuals, and its professional edition costs $10/month or $100/year per user.
