I got the error on Mavericks: "DVD Audio Extractor" can't be opened because it is from an unidentifed developer. What can I do?

This is because of a new security feature called Gatekeeper added lately in OSX. It by default restricts apps from running if they haven’t been downloaded from the Mac App Store.

To get around, right-click (or control-click) the application icon and choose “Open”, click the “Open” button at the next dialog warning to launch the app.