NaviActionPad is a navigation and action execution plugin.
By pressing Alt F11 you bring up NaviActionPad's popup window which shows the currently selected element (class, method, directory etc. in the current editor or project view) and its siblings.
You can navigate through the hierarchy by pressing the left cursor key for the parent and its siblings and by pressing the right cursor key for the children of the currently selected element.
Pressing CTRL and the right cursor key will bring up a list of available actions that can be executed on the selected element.
Pressing Enter will either execute the selected action - if one is selected - or open an editor for the selected element.
This plugin has still a way to go till it is finished, but I think it's already useful in its current state.
What to expect in the next releases:
More actions. Currently there are a few refactorings (Rename, Move, Change Signature etc.) and "Find Usages" available.
Filter. Currently you only see a seemingly useless textfield below the list. This one will contain the filter that will be applied to the list contents.
The label above the list shows the context of the list - its parent. Now its only a simple toString on the parent PsiElement. The next release will equip it with an icon and the same text representation that it would have in the list.
I think this is a new and useful approach to navigating through a project. You only need to know the one shortcut - Alt F11 - and can navigate around a project and get presented with a list of applicable actions - no matter whether they are refactoring or some other kind of action. There's no need to search through menus for the refactoring or action you want to execute.
It certainly partly does what NavigationBar already does, but it also navigates to methods and it has a fixed size - no matter how deep your package structure may be.