The only one that comes to mind is Nagios (http://www.nagios.org
), and only because I read about it recently. Have not used it myself, though. Needs to run on an Apache server if I understand correctly. Not sure if it's exactly what you're looking for.
EDIT: GTrace looks more like what you're after:http://www.caida.org/tools/visualization/gtrace/
but not in Portage and no ebuild in the Gentoo Bugzilla either, so you'd have to create your own ebuild.