The Multi Router Traffic Grapher (MRTG) is a tool designed to monitor the traffic load on network-links. In practice, it can be used to graph any trend for which continuous data is available either via SNMP or another external program. The campus network is more likely to need to record traffic levels but other host-specific resources such as file descriptor use etc. could be graphed using MRTG.
An example graph based on 30 minute traffic averages over a week is shown below.