An in-game notebook for scribbling down notes, todos, player notes, kill list, etc.
Each character gets their own notebook & there is also a notebook shared among all characters.
Very simple & lightweight. No settings. No features. Just a WoW-style notebook (see screenshot).
You can set a keybinding to open your notebook. I have mine set to K.
You can also open it with /notebook or /nb.
Can't believe this has never been part of the standard interface!