de.nellessen.usercontrolleddecryptionoperations

This software enables you to transparently encrypt your Dropbox folder on your PC. It also lets you confirm the decryption operations on an Android smartphone, which is used as an NFC-enabled token. Additionally, it supports sharing files with other Dropbox users, while still encrypting the shared data. To really use the app, you also need to install the encrypting program on your PC. It can be found in the source code repository.