Crumbler Navigation Tool
The crumbler tool, shown above, allows developers to fit a tree-based navigation system into a 'breadcrumb'.

[VERY HASTILY WRITTEN NOTES BELOW, MORE FOR MY OWN REFERENCE]
If implemented on every page, the tool provides users with a consistent and easily visible display of their current position within the site tree. It also allows the user to rapidly access to any level of navigation.

Comparisons
Traditional tree-based menus have required the user to click on each tree item, or more frequently, to maintain a high level of mouse-control, where one movement can 'undo' or reset the navigation back to its default state. These systems also generally expand along the vertical and horizontal axes, and are not suited to sites with more than three levels of navigation.

In order to provide a user with an idea of where they are in the tree, a traditional system must either be augmented with external visual cues, or must remain expanded, taking up valuable screen real-estate. If a menu is 'stored' in a collapsed state, however, the user must navigate through the menu structure each time they want to access items within their current level.

Crumbler addresses these issues by providing a menu that exists as a breadcrumb trail in its default state, yet can be turned into a tree menu by positioning the mouse cursor over one of the crumbs. The menu that appears is relevant to that level of navigation, so for example, a user moving their mouse over the last (rightmost) crumb would be presented with a menu containing pages within the current section.

If a menu item contains a submenu, it will shown in the next menu position to the right, aligned to the top of the crumb trail. Upon moving the cursor to this new menu, the previous menu collapses, and the parent menu item appears as the preceeding breadcrumb. This is repeated if a user enters yet another submenu. The effect of this is such that when a user is at the menu item they want, the breadcrumb trail shown looks exactly like the breadcrumb they'll see on the page they're going to. This 'preview' breadcrumb trail is italicised to show that the user is in 'navigation mode', and to prevent confusion with the default breadcrumb showing the current location.

Within a menu, a user can move their mouse out and to the left to access the preceeding menu system, so if a user mistakenly enters a submenu, they can simply move back and choose a new one.

Issues
As each submenu is aligned to the top of the breadcrumb, and not to its parent menu, there may be situations where a user will have to move their mouse into 'empty space' before moving the cursor up to reach the submenu. While crumbler can handle this, it is counter-intuitive.

Similarly, most users will not be automatically aware that moving their mouse to the left of the current menu will activate the parent menu, and may choose to renavigate through the menus instead.

Technology
Crumbler is coded in JavaScript/CSS, and will work in IE5+, NS6+ and Mozilla on both PC and Mac platforms.

The menu is controlled via a javascript file containing various arrays, one for each menu item. The default breadcrumb for each page is based on yet another user-defined array located within the same page.

Download Source + Example (4kB .Zip)