How are HTML apps and add-ins associated with each other? (Can HTML apps trigger add-ins to be launched?) HTML and add-ins can both be part of the same application, that is each is a different entrypoint of the application. The association takes place at registration time, when both would be registered as one application. An HTML page can start an add-in (on-demand only, not background) by using the NavigateToPage function with the guid for ExtensibilityEntryPoint as the first parameter.
Is there a way for HTML apps and add-ins to exchange information (parameters) and trigger events? (Is it possible for an add-in to be registered as a listener to an event that is fired within an HTML application?) No, there’s no built in way for add-ins and HTML pages to communicate.< Communication between a background add-in and an HTML page could be achieved with an ActiveX/.NET control on the HTML page and then .NET Remoting between the two components.
How do I register a .exe file so it runs from More Programs? The same way you register an add-in, except instead of using the “addin” property on the entrypoint tag, use “run” with the path to the .exe