Eight great virtual appliances for VMware, free for the downloading

Opsview monitoring
Opsview Community Edition 3.8 is free, open source enterprise network and application monitoring software that is available as a virtual appliance for VMware player. However, it can be converted to run on VMware ESX or ESXi by using the free VMware vCenter Converter tool.

Opsview is built on Nagios, an open source enterprise management platform. Opsview adds enhancements to notifications and alerting (both in terms of controls and methods), support for SNMPv3 with MRTG, flap detection, faster importing, and improved uptime checks. In addition to the VMware appliance, Opsview Community Edition can be downloaded as source or binaries for RHEL 5, CentOS 5, Debian, Ubuntu, and Solaris 10.

Opsview offers some unique features that make it a formidable management tool, such as support for monitoring virtual servers and a variety of hardware components found throughout the network. Normally, an advanced management tool like Opsview would be difficult to install and configure -- however, most of the pain of installation is eliminated with the virtual appliance version of the product, where initial setup takes only a matter of minutes. The browser-based GUI is informative and easy to navigate, making it a snap to add devices to be monitored and to define dashboards that offer meaningful information. The Community edition is offered under a GPL license, while a more advanced version of the product that includes support is offered under a subscription model. Managers of smaller, simpler networks may find everything in the free version to meet their needs.

Cacti is a network monitoring and performance graphing tool that works with SNMP to capture what is happening on the network and present that information in easy-to-understand graphs. As with any network monitoring tool, Cacti can be somewhat complex to set up, because of the dependencies on MySQL, PHP, and other components. However, for those administrators who want a visual representation of what is happening on the network performance wise, it is pretty hard to beat the flashy, informative charts that Cacti can offer.  

Cacti works by polling all SNMP-capable devices on your network and adding the information you've selected to graphs. In its simplest form, Cacti will give you the ability to create graphs for the most common aspects of host monitoring, such as disk space, loads, memory usage, NIC monitoring (bytes in/out of an interface), and so on. The browser based management console is nicely done, and plenty of support is offered on www.cacti.net.

Downloading Cacti as a virtual appliance avoids a somewhat complex configuration process that includes creating a virtual server, installing CentOS, and configuring Cacti. However, preconfigured virtual appliances usually cost a few dollars, as opposed to being free. An example of that would be the JumpBox version of Cacti, which runs $49 or $99 per month; a 7 day trial is available at no charge if you want to give that implementation a try, before going through the manual steps to create your own appliance.