is an Open Source web analytics platform. This gives you similar statistics as Google Analytics with full control over all aspects of the data collection and reporting.
Piwik gives you a huge amount of control over the collection and display of statistics and has a great plugin API for customization and integration. I used this to do some direct integration with Elgg. This allowed me to build reports based on specific inteactions within Elgg, and to collect stats such as most active users, most interesting content, and to build client specific reports for user activity.
Piwik also allows embedding the reports and graphs within another web page, so I was able to integrate the Piwik reports along with custom report data generated within the Elgg platform to show the analytics within a custom Elgg administraive user interface. The user experience for Elgg administrators allows them to view all the analytics without leaving Elgg or using another login.
Piwik offers great potential for intergration and custom analytics for any web platform.