window-navigator
The Window Navigator Object contains information about the browser and is a property of the window object.
Clipboard API
There are far more aspects to the window.navigator object such as being able to address the Clipboard via the Clipboard API.
Checking if the browser is online
This would be useful if I am using styles and fonts that I am accessing from the Internet.
When developing off-line (i.e. locally before uoloading the file to the server) I normally have Internet access, I change the linking of the W3 Framework to a local copy.
Finding your location
geolocation