I'm looking for a piece of software which I can install on my client's Windows based servers which does the following:
1) Runs as a Windows Service
2) Monitors basic system health - CPU usage, Hard disk space, memory usage, the running state of services or tasks running on the server, RAID array health etc.
3) Monitors typical online services - HTTP, FTP, VPN, Ping tests etc.
4) Reports anomalies by sending an email
I'm looking for something fairly small, lightweight and simple, and hopefully free or open source, which I can install on all my client servers to warn me of servers that are about to run out of resources, or which are having service problems.