The generic container framework was introduced in Notes 8.5. The framework is based on Eclipse extensions so just like the Web Browser, Notes Document, Notes View, Symphony Spreadsheet, and the Open Span containers, you too can create your own container.
Mike Cooper published a pretty in-depth article on how to do this. This is not for the light-hearted and to be honest not many companies/people should be creating a container. You might want to check out the first link the article that explains the difference between components and containers before diving on the main article.