JFFNMS (Just For Fun Network Managment Service) is another tool like MRTG and Cacti which act as a web frontends to RRD graphing. JFFNMS concentrates on SNMP collection, and has builtin ability to monitor most managable snmp capable switches and Unix PC's running snmpd.
It is available from http://www.jffnms.org and is written in php
Notes available on JFFNMS from the wiki:
One page links to JFFNMS: