List all Configured Menus in the System Is there a developer tool, module, or code snippet that will show all the menu items currently configured in a Drupal system?

If not, would it be "safe" to invoke the menu hook myself to collect this information?  In other words — do individual menu hook listeners (implemented by module developers) alter system state in such a way that invoking the menu hook twice during a page request would be a "bad thing". 

Newish to Drupal, not new to programming. I'm specifically interested in a programmer's view of the menu.
You could use menu_get_menus, or use a modified version of its code:

https://api.drupal.org/api/drupal/modules!menu!menu.module/function/menu_get_menus/7

It returns an associative array of the menus names, either the custom one, or also including the system menus.