I watch a lot of YouTube videos and have found it very annoying that YouTube latches onto one or two topics that you've watched and only recommends that type of content over and over again. Even if you use their "Not Interested" tool, not a whole lot changes in your recommendations.
At the end of last year I launched Relevant - a crowdsourcing website where users can categorize the channels they watch into a defined hierarchy of categories ranging from broad topics like "Science" and "Gaming" to more specific ones like "Phone Reviews" or "Speedrunning".
Although I've had good feedback on the website, engagement has been relatively low and I think that's because it's a big ask to have someone navigate to the website to find the content. This year I decided that I'd bring the content to them by making a Chrome extension that lets users interact with Relevant directly from within YouTube.
It's still a work in progress but I'd love to get a first version out within a month or so to start spreading the idea and gathering feedback. If this is of any interest to the people here on HN then please let me know what you'd like to see most on your feeds.