A slot layers system by Steph
First slot show all the objects in the view
the others slots only the objects inside them self
Possibility to select some slots in the same times by pressing a key(Shift + click ?)
Possibility to colorize a slot who gives this color to it objects inside
Little icons for properties display, and an lock icon
Steph

And I presume possibility to move an object from a slot to another slot :)
Have fun :)