WassUp is a Wordpress plugin to track blog visitors in real time. It has a very readable and fancy admin console to keep tracks of blog's users visits.
It has a "current visitors online" view and a more detailed "visitors details" view where admin can know almost everything users are doing on the blog, it's very useful for SEO or statistics maniacs and it has a "Spy" view in Ajax like the Digg Spy.
The aim of WassUp is the knowledge of what the visitors do when they surf the blog. With WassUp you'll get a cronology of your blog's visits with a lot of details for each single user session and some charts.