As for the mechanism part, I could not comment on anything existing without knowing what platform or technology it would integrate with... Drupal? Wordpress? Craft?
The "Table of Contents" structure is universal (and should dictate the layout of all web content).
It is straightforward and logical.
If a table of contents is too long, we can apply structure and behavior to our application to help.
e.g. pagination, collapsible sections, indexes...
My answer would be to display all user-facing web content with the Table of Contents layout in mind, then use IA to dictate how our interactive layers will provide a more usable display.
Then we can ask:
How can I divide/structure my table of contents information in a way that's easy to use? And, if applicable, do I need any behavior layers to accomplish my goals?
And a "Defensible" version of the question might be:
Does the structure of this table of contents allow users to find what they need in less than 3 clicks? 2 clicks?
With this in mind, if you have a really deep menu, I feel it best to use a relative subset menu. One that only shows the current section of the menu tree. And long menus usually fair better with a vertical implementation (in the sidebar).
This would be based on a breadcrumb menu (probably built off taxonomies), which would also be your "main" category presentation.
The breadcrumb menu shows me the chain I followed (and allows me to go up the chain), the submenu shows me the current options available (allows me to go down the chain).
"Ajax-ing" content would probably find a good use case here.