http://msdn.microsoft.com/en-us/library/cc289775(VS.85).aspx" title="OpenService Accelerators Developer Guide">OpenService Accelerators Developer Guide Accelerators are contextual menu options enabling quick access to applications/services found on the web. Accelerators appear on the right-click shortcut menu of the Web page in Internet Explorer 8. They are grouped by function so that users can quickly access the task that they want. Accelerators enable two types of scenarios: users can "preview" information without leaving a Web page or "execute" to send content directly to an application or Web service. An XML-based Accelerator uses XML file to describe the format of HTTP requests to the Web server. Data from the target context (selection, link, or document) is passed as variables in URL parameters and/or form data. To install XML-based Accelerators from a Web site, use the window.external.AddService method to prompt the user. Accelerators allow users to act on data on a Web page. Accelerators are declarative. They use HTTP submission to communicate between the browser and the Web site. XML-based Accelerators are easy to create, test, and deploy to users. Categories Accelerators are grouped by function so that users can quickly access the task that they want. You can set the default Accelerator for a given category when you install the Accelerator or through the Manage Add-ons dialog box. Examples of services that exist today: Add: del.icio.us, Digg, Reddit Blog: Windows Live Spaces, Windows Live Writer, Blogger Define: Encarta, Wikipedia, Dictionary.com Map: Windows Live Map, Google Maps, Yahoo! Maps, MapQuest Send: Windows Live Mail, Google Mail, Yahoo! Mail Translate: Windows Live Translation, AltaVista's Babel Fish, Google Translation If the Accelerator doesn't fit a recommended category, you can define your own. 

<os:activity category="Share">
The category should be a verb that the user can recognize and is not tied to a specific brand or application so other Accelerators of similar functionality can use the category. Additionally, because the value of the category attribute is used by Manage Add-ons to organize Accelerators in groups, it should be human-readable and capitalized appropriately. Variables Document properties and content are sent to the Accelerator service provider through HTTP GET and/or POST submissions. These properties are expressed as replacement variables that can be passed as form fields or as URL parameters. Variables can be specified directly in the action attribute of os:execute and os:preview (called a "URL template"), or within os:parameter elements. Note You can use cookies to store state and user credentials.