Preinstalled virtual disks for VMWare.
"A virtual appliance is a fully pre-installed and pre-configured application and operating system environment that runs on any standard x86 desktop or server in a self-contained, isolated environment known as a virtual machine. Virtual appliances provide an evolutionary step in the software distribution model." (quote from vmware.com)
One of many available appliances is vehera-base, a Mediawiki appliance.