This RRDTool Framework provides a central HTTP-based service for import into standard RRD DBs and graph generation. A lightweight, easily extendable agent for the data sources is pushing updates with minimal resource consumption on the master service.
Serverstats is a simple tool for creating graphs using rrdtool. Serverstats does not have any features to manage the created rrd-files, if you change anything you have to delete and recreate the files. Perhaps you can avoid this using third-party-tools
System and Network Monitor (SNM) will monitor and graph computing devices using snmp, ping & custom modules, also alerts via email. SNM is written in Perl for Win32 & Linux, runs 24*7, recording results in RRD for later display via a web browser.