gNotify no longer exists, but a replacement has been issued by Google itself.

You can download Gmail Notifier at this location.

gNotify is a FREE Gmail utility that runs in your systray and notifies you when you have new Gmail.

There are a few ways to be notified including balloon tips, audible alert, or any combination of the two.

gNotify can be configured to check for new Gmail as frequently as every minute, and shows a preview of each new Gmail on the View Mail tab.