ReadWriteWeb

Google Analytics may be free, but it is still based on proprietary technology - which means you only ever get reports on the things that Google thinks are necessary and some of those reports are aimed at people using Google's other services (managing campaigns on AdWords, for example). Further, using Google Analytics means that you're tied to Google's TOS. Enter Piwik, which aims to be an open source alternative to Google Analytics. It is closely affiliated with OpenX, the open source ad server alternative to Google Ad Manager [Ed: which we just started using on RWW].