NRG is a system for maintaining and visualizing network data and
other resource utilization data. It automates the maintenance of
RRDtool databases and graph web pages (that look like MRTG web
pages.) NRG is primarily configured using very terse meta-
configuration strings. These strings tell NRG to autodiscover
network devices and verify that their current NRG configuration
is correct.

WWW: http://nrg.hep.wisc.edu/