Google Analytics is a service offered by Google that generates detailed statistics about a website's traffic and traffic sources and measures conversions and sales. Google Analytics can track visitors from all referrers, including search engines and social networks, direct visits and referring sites. It also displays advertisin...
StatCounter, a free online visitor stats tool. It offers its members the chance to grow and improve their online businesses by allowing them to monitor the number of hits to their website; the geographical location of visitors; the various pages a visitor views; keywords used to find the site plus other features.
nginx [engine x] is a HTTP server and mail proxy server written by Igor Sysoev.