The functionality of this app has been superseded by the YubiOATH app: https://play.google.com/store/apps/details?id=com.yubico.yubioath
The new app allows multiple OATH secrets to be stored and does not require the use of the YubiKeys slots. Note that the new app does require the installation of an applet on the YubiKey NEO device itself. Instructions on how to do so can be found in the description of the YubiOATH app.
This helper App allows you to generate OATH TOTP codes with the secret [or seed] stored in a YubiKey NEO’s secure element. Using this App, you can use 2-step verification with services such as Google Apps/Gmail or DropBox without having the 2nd steps’ secret stored on your Android device – this is a concern to many who are using the same device to access the service.