Not really a specific tool. We write all our analytics out and then do some rollups in the database and use Highcharts to display them on the website. Not super fancy, but effective. For our setup its more about the process to rollup the data than a specific toolset. We wrote all our own metrics and tracking using a middleware concept with Express in node.js. That's probably not totally relevant to your use case.

Hopefully that helps a little. Let me know if I can help you any more, happy to share whatever I can.