Some of what Project Proteus makes possible is already doable with Skyrim's console commands and existing mods, but this brings it all together in a single pop-up menu.
It also lets you edit NPCs and items, even the weather. NPCs who have died remain dead, items left in storage can be retrieved, and so on.
While you could switch to another savegame to play your Khajiit archer for a while, Project Proteus lets you import your characters into an existing world state-meaning you can switch to a character with their own items, skills, and spells, but keep your current quest progression.
