Swarm seems like a very unique idea, from the main page you click on "go use swarm" what appears is a bunch of of little screen shots of various sites, as far as I can tell when someone leaves one of these sites and goes to another site, the site they end up on also appears as a thumbnail and so on, it keeps growing as more and more people go to other sites.
Its a real time representation of where people are going.
Also from the main page you can download an extension for firefox, this is what Swarm uses to track movements and sites. Its pretty quick and doesn't seem to take up any resources
This thing just keeps getting bigger and bigger. I got pretty hooked up on watching one busy trail just to see where they went next.
Main page of Swarm
Swarm, Website, Map, Firefox, Extension, Unique