Armor Stands. The left one is specific to Bibliocraft
The Armor Stand is an item found in Bibliocraft (and currently one other mod) that holds and displays one set of armor. Right-clicking the stand itself will display the UI. The UI shows the armor on the Armor Stand, the armor the player is currently wearing, and the player's inventory.
There is another armor stand, and it is part of the Better Storage mod. Details on that Armor Stand can be found here.
Comparison of the two armor stands. Bibliocraft stand on the right, BetterStorage on the left.
In order to open the GUI on the armor stand, right click it with your mouse. This will open up a menu showing both its respective slots for armor, as well as yours, for easier use. If you wish to 'Quick Swap' your armors, Right click it while crouching.
You can also place Backpacks on the armor stand, however it does not display color, or even differentiate between large and regular backpacks.
An Armor Stand equipped with Diamond Armor.
For example, then, if you're wearing the Monocle and wish to take a Kreknorite helmet off of the armor stand, leave your hand open and shift-right-click the helmet on the stand. The monocle will now be on the stand and the Kreknorite helmet will be on your character.