You will need to install a user script manager extension to install this script.
Just a very basic script to save video times, and display a list at the top of the YT homepage to resume the videos. By default, this saves the video's position every 5 seconds. If within 30 seconds of the end of the video, it's assumed watched completely and forgets it. A "Forget" button is added to the top-right of a video page, if you don't want it to continue remembering the position.
This was just made quickly and poorly, to solve a personal annoyance of finding watched videos/resuming when opening several videos paused in the background and watching them as I get to them.
The UI is admittedly ugly, but it works for my purpose -- quick and easy.
I attempted to find something like this and couldn't, so I quickly wrote this up and decided to share just in case it's useful for someone else.