Show JS(jQuery) widget on any site, with ASP.NET MVC server side [duplicate]

Answer 1

Look at this SO post jsonP and the ticked answer provides an example of pretty much what it sounds like you want to do (in MVC / Javascript)

Answer 2

Check out the following blog entry, it helped me a great deal while developing something similar

http://alexmarandon.com/articles/web_widget_jquery/

In general, keywords for you are dynamic javascript and css loading and JSON-P that enables getting around browser's same origin policy while sending AJAX requests.