Alexa provides information about websites including Top Sites, Internet Traffic Stats and Metrics, Related Links, Online Reviews Contact Information and Search Analytics for SEM and SEO optimization. The Alexa Toolbar is a browser add-on that shows data about sites as you surf the web
piwik is an open source (GPL license) web analytics software. It gives interesting reports on your website visitors, your popular pages, the search engines keywords they used, the language they speak… and so much more.