Server monitoring? [duplicate]

Polymon is exactly what you're looking for.

It's fantastic for monitoring anything that can be communicated by TCP Port, SNMP, Powershell, WMI, SQL, HTTP, Perfmon, or Ping.

I don't monitor anything *nix, so I can't speak to that. But for the Windows world it's very simple to set up, extremely intuitive, and extremely flexible, It has very nice built-in dashboard display, sms or email notification. You can do long-term trending/reporting/graphing, auto respond to events (like restart a service if it stops, etc.)

And at least for me, it's a lot easier to set up and maintain than Nagios, OpenNMS, or Zabbix. I heartily recommend it.

Zenoss

Nagios can monitor process in memory (so services too) through snmp. So you don't have to install the nagios agent.

OpenNMS & Hyperic both work on Windows and are open source. Hyperic has a for money option but the basic offering is open source and free. Both are Java based.