Hierarchy
Hierarchy is a little Mac application that I wrote in 2007 and no longer maintain.
When Mac OS X 10.5 Leopard was first released, the Dock lost the ability to click a folder and get a hierarchical menu of the folder’s contents; instead, it would only show the “stack” view. I wrote Hierarchy to create a little Dock replacement that restored the functionality.

I figured (hoped!) it would only be a matter of time before Apple restored the functionality in the Dock, and as soon as they did, I stopped maintaining Hierarchy.
If you’re curious, you can still download Hierarchy v1.0.4.