Platform: Windows Phone
Authenticator is Microsoft's solution for its Windows Phone users. The app works wonderfully with Microsoft, Google, and Facebook accounts. It's very easy to set up the authenticator in the respective account settings. Once set up, Authenticator will randomly generate codes to be used in conjunction with the account password. So if someone tries to log into an account with the password, they'll still be prompted for the Authenticator code which is only available within the app.
For the security conscious, this is a fantastic solution to the always growing problem of account security.