StatPriorityTracker uses your own input (and saves it per character) and displays it in a frame next to your character's equipment screen.

You can toggle the view by pressing the "SPT" button at the bottom of the equipment screen.

 

Despite the name, it's not necessarily strictly for stat priorities these days (I originally had made this addon in retail and ported it over to Classic). Back then, I used to update it very often with actual stat priorities baked in for all classes, but it turned into a full-time job really fast and I couldn't keep up. Instead, nowadays it is a convenient little toggleable notepad attached to your character's equipment screen and you can type in whatever you want (but make sure to include manual line-breaks).

 

The toggle button is draggable. Simply hold right-click on your mouse and drag away! To reset it to the original position, there is an option in the settings.

 

Known issues

- If there are any problems (or if you have any suggestions), let me know!

Screenshot