Summarize.tech is a blissfully barebones website that takes a YouTube URL and, in seconds, spits out what appears to be a good summary of the content of the video.
I tried it on the 1976 documentary about a New York gang I posted yesterday and here are the results. I also tried in on Tim Urban's TED Talk about procrastination and here are the results. The website appeared to work well for both videos I tried.
For the documentary, it accurately summarized the content, and for the TED Talk, it accurately captured the main points (with a few small errors). I could see this tool being useful for busy people who want to quickly get the gist of a video but don't have time to watch the whole thing.