With vSphere 4 it is possible to create your own vSphere Plug-ins based on the .NET framework. These plug-ins work in combination with the vSphere Client, like the Update Manager or VMware Data Recovery. So the plug-ins enhance the vSphere Client to a single management tool for different business needs.
Christian Johannsen over at mightycare:
In the past some of our customers ask for integrations of their management tools or own web application in the vSphere Client. The easiest way to include web applications into the vSphere client is to use the .xml definition. The problem with this solution is the static definition of the contents. So we decide to develop a webservice plugin which is dynamic, based on the clicked object in the vSphere client (MoRefID) and allows you to define which application is deposited for this object. The plugin consist of two parts:
• the plugin for the vSphere client
• an example WebPage (index.php)
The plugin is used to configure the path to the webserver and the webpage is used to show an example for the MoRefID (Managed Object Reference ID) handling.
In this version the following managed objects could be used for web-applications:
• 
virtual machines
• resource pools
• host systems
• cluster
http://www.mightycare.de/aktuelles/mcswebserviceplugin_veroeffentlicht
