According to piwik.org,Piwik is a free software alternative to Google Analytics that is used on more than 320,000 websites.
If you are interested in using Piwik with your concrete5 site, check out Adrian Speyer's informative article about how to get the most out of your Piwik installation when you are using concrete5.
Read the full article at Stat Story:http://www.statstory.com/concrete5-and-piwik/