Wiitar

Wiitar connects a Nintendo Wii Guitar Hero controller to your Mac. Now you can play Frets on Fire, record directly into GarageBand, or use the guitar with any other application.
Wiitar maps the buttons of the Wii guitar controller--including the Whammy Bar and Strum button--to any keyboard keys.
For each of the color keys, the Whammy Bar, and the Strum button, enter an alphanumeric key or select a special key from the list.
The Whammy Bar slider sets the activation level for that key--the higher it is set, the further you must push to send the key.
"Send Keys on Strum" waits until you press the strum button to actually press the keys (as in the Wii game); "Send Keys Immediately" activates the keys as soon as you press the buttons (for Frets on Fire).