The Multi Router Traffic Grapher (MRTG) is a tool to monitor the traffic
load on network-links. MRTG generates HTML pages containing GIF images which
provide a LIVE visual representation of this traffic. Check

http://www.ee.ethz.ch/stats/mrtg/

for an example. MRTG is based on Perl and C and works under UNIX and Windows
NT. MRTG is being successfully used on many sites arrond the net.