HealthMonitor is a free powerful and featureful system monitoring tool for Windows.
It works as a Windows Service and check system status (event viewer, disk free space, services status, performance....) and notify the administration by E-Mail, SMS ...
Sadly this project is dead. However a more flexible replacement suitable for networked PCs inspired by HealthMonitor is AuditQi is now available on sourceforge (or google AuditQi). Major sources of health information include Event logs, The Registry, WMI windows management instrumentation, Windows Update (especially useful for networks not running WSUS), Windows Security Center alerts - Antivirus Status/Firewall/AntiSpyware/UAC/Login Provider, File Versions especially EXE files and XML settings files content. Health assessment can also include behavioral activity ie Time since last restart or applications installed ie flash. While healthmonitor is useful for monitoring a single PC AuditQi monitors PC and server health across your network.