I downloaded a course and ran into the problem of tracking my progress and remembering where I left off. Instead of sitting down and finishing it, I found a way to procrastinate — so I made a tool that keeps track of exactly where you left off in a video, which video and chapter you're on, and lets you take notes and add videos to favorites. Now I can go back and watch the course. I have no excuse. The app is open source, so now you have no excuse either. https://ckourse.com/