Big brother is a well matured product with an easy to use web based interface that quickly with color marks shows what is good or bad. Big brother is available in a free version only for noncommercial use. This is also available for evaluating in your environment.

With a software installed in the clients you can add functionality and see more things that are not available by snmp like disc and cpu usage, what services are running and there are historic views for every machine.

Download Big brother here