That is a nice analytics program you found, wonder if it could be ported to a extension though, reading the
http://piwik.org/docs/installation/
edit: installing it, *caramba!* over 6000 files
edit2: installed it, and glued the code in the google-analytics extension
Actually, an extension needed for Piwik Analytics (and many more usefull things) would be an extension tot add custom code to the footer of the page, just before the
</body>
tag.
Maybe in the same extension also the possibility to add custom code in the header, just before the
</head>
tag.
edit3: made an extension request which would also suit this request :
inject custom code to header and footer