Probably Google Analytics/urchin.js, among others.
It’s just a hit counter that collects some other details; operating system/browser, IP address, and some public browser variables.
The rest of the information GA collects is derived from the IP address: country of origin, ISP, physical location (city-level, unless GPS is turned on.), &c.
Most web page hit counters do this now; as such, most ad/script-blockers block them.