It's not. It's a different app. It just happens to be installed on your site using JS.
Because with Google Analytics, you can't personalize an session.
actually you can personalize a session.. you would need to parse the __utmz and other cookies set by GA.
but this one provides a simple set and an easier way to do it.
It seems to me that this provides information real(er) time than GA. As in, you use it on pages as part of the actual data you show: http://www.visitorjs.com/details/api/setup