iiToad is a very easy to use application designed to be an usage meter for the Australian Internet Service Provider iiNet, that has been developed in cocoa for Mac OS X.
This program has been designed to either run in the menubar or in a floating window, and displays ADSL data usage, as well as providing links to iiNet websites and a built-in radio player to listen to quota free streaming radio stations.
The interface is completely customisable, so you can have just text in the menu bar (such as % of total quota used), an icon, or a whole range of different menu widgets.