Need trends? Try Cacti.

This blog post by Paul Venezia introduces Cacti, an alternative to MRTG: Need trends? Try Cacti.

I'd played with Cacti years ago when it was in it's infancy. Now, it's all grown up. The newest version supports the most common data gathering tools, and has facilities for custom additions, however Byzantine the structure may be. If you want to graph router/firewall ifInOctet/ifOutOctet data, that's simple. Graphing CPU utilization from Net-SNMP hosts is equally simple, and built into the base distribution. Adding custom data is a bit of a challenge, as it requires intimate knowledge of the inner workings of Cacti, and a bit of a brain-bend on how exactly the Cacti magic happens. Make no mistake, you will need to make several attempts at custom code unless it's simple SNMP queries. The usage of non-SNMP data for per-instance queries is decidedly non-obvious.