Healthmonitor is a free powerful and featureful monitoring tool for Windows.
It works as a Windows Service, monitor system performances/thresholds (CPU load average, free memory, disk space, Event Viewer…) and handle specific check plugin (Check HTTP, windows services, custom script).
It can log result on a database or send a notification by E-Mail, SMS, PopUp…
Requirements: Windows 2000 or greater with .NET Framework 1.1