Munin is a tool for graphing all sorts of information about one or more servers and displaying it in a web interface. It uses the execellent RRDTool (written by Tobi Oetiker) and is written in Perl. Munin has a master/node architecture. The master connects to all the nodes at regular intervals, and asks them for data. It then stores the data in RRD-files, and (if needed) updates the graphs. One of the main goals has been ease of creating own "plugins" (graphs).