A few years ago (ok a LOT) I had written a VERY simple network monitoring system for work. It primarily gathers syslog events, and does a basic TCP connect to check on machine state. This uses MSDE as it's engine for events.
Cacti is a complete frontend to RRDTool. It stores all of the necessary information to create graphs and populate them with data in a MySQL database. The frontend is completely PHP driven.
Please check out the official website for the latest releases.
MySQL Check & Backup & Notification
This is a script that check, periodically the tables of a MySQL Server. Using the BACKUP, CHECK, OPTIMIZE and ANALYZE, the script checks if everything is ok and alert you if anything is wrong.