A look at the history of open source monitoring tools, an attempt at fixing our vocabulary within monitoring, and a proposal for the "event stream model" as the future of open source tooling.

Similiar to MRTG graphs showing Network Usage, Munin is monitoring system used to produce graphs of usage of key areas in the running of a server. Munin can produce graphs of:

Disk Usage
Mysql
Network (similar to mrtg)
Postfix Mail
Processes
Squid Proxy
System - CPU, Load, Memory etc.