Tried browsing through forums and other sources, but having trouble finding a mod that I swear I saw someone using once. It isn't the mod My People, nor is it the custom NPCs mod as far as I can determine.
I don't remember the specifics, but the mod essentially allowed you to create a sort of dummy player body that you could switch control to allowing for quick swapping of inventories, locations, ect. When a body wasn't being used, it would just stand there and do nothing, but could still be killed if not left in a safe place. Essentially allowing you to exist as two or more different bodies within the same world.
I don't know of the state of the mod, or if it was just a WiP at the time, but must have seen it sometime in the last 6-8 months since I was taking a break from playing when I saw it being used. But it looked like a unique mechanic to play with, especially when you have situations where you want to quickly swap between multiple roles on a single player world without having to go through the trouble of clearing inventory every time.
Seeing if this sounds familiar to anyone else who might be able to help track down this mod.