StatCounter is a popular web analytics tools that is available for free use for a limited number of data per day.
It has a high popularity and users are able to add multiple sites and view different statistics, including on traffic sources, exit links, download activity, visitor map, their country and city, length of visit and the entire path of a visitor on your website.
It offers a lot of data in a very intuitive interface, site owners are able to view and customize graphs by period and other details (page views, unique visits, returning visitors and more).