Right now for only iOS and Macs (though Windows and Linux are in development), FingerKey is a £1.49 app that lets you login to a Mac using the fingerprint sensor embedded in iPhone 5s, 6, and 6 Plus. The password is shared between devices using AES 256-bit encryption, which is the highest key length for that standard. FingerKey and FingerLock, the Mac companion app, work together to give you unlocked access to several different computers. You can also access the TouchID widget in the notifications pane for quick login (thus skipping the extra step of having to launch the app, etc).
Here's a quick demo: