> that you could click through the interface and find a lot of capabilities that were vestigial

Lotus Notes allows you to right-click on a "document" and see absolutely all data attached to it, directly in the UI, including access permissions. This can be immensely useful, because not all data could be part of its UI representation.

The closest to this today would be inspecting the JSON data on your browser networking tab to view what your app exchanges with the server, but its much more clunky.