Web Plugin Architecture required

Hello, I look for a list of web-applications that support user-uploaded extensions. So a user can upload an extension which will be available either on the apps marketplace or just for the user privat Hello, I look for a list of web-applications that support user-uploaded extensions. So a user can upload an extension which will be available either on the apps marketplace or just for the user privately. What other Apps like this exist ?Also, is there a framework that supports adding this functionality to a new Web-App ? Ideall...