MATrackingArea

MATrackingArea provides a free category on NSView and an accompanying class which together allow you to add “tracking areas” to your views.
Tracking areas are like tracking rectangles but are more robust and effective, and can be configured to track the mouse either at all times, only when the view’s app is active, only when the view’s window is key, or only when the view is First Responder.
You can also choose whether to use the view’s visible rect in preference to the rect you pass in. See the example for details.
Fair warning: MATrackingArea uses a polling timer to do its thing, but in the tests it consumes very, very little CPU (0.1% in Activity Monitor), and it will only poll if there are actually some tracking areas set up.

System requirements:
- Xcode 2.4 or later