It seems Arsonide is on a mission to spam the community with high quality plugins. I can't say I disapprove of course.
His latest plugin Data Structures provides you with three new objects: Stack, Queue and Deque. What these exactly do can be found out from the detailed description in the official plugin thread.
But let me try to find some own words to describe the functionality: think of it generally as a way of organizing a group of elements lined up in a single row. Now you can add to that, either in the back or the front, and you can remove as well in the same manner. At least that's true for deque.
With the stack you just add and remove elements at the front, while queue adds to the back and removes from the front. If I'm not completely mistaken deque can actually do everything that stack and queue can, and then some. There are also more expressions available to deque, like getting an element at a certain position.