Rex doesn't need agents or a special language to describe the tasks it performs on remote computers.

Although Nagios gets lots of attention, the popular network monitoring tool Zabbix is free, can configure hosts for direct monitoring in the web interface, and now can also monitor VMware machines in version 2.2.

Virtual machines seem to be ideal for spare capacity. They are easy to create and remove – if only all those time-consuming administrative tasks like assigning IP addresses, setting up backups, and monitoring were more manageable. Having the right tools can help.