It took less than a year for youtube-dl (2006) to spring up after YouTube (2006) was created. youtube-dl is an open-source program that, well, downloads YouTube videos for free. Any format, any quality, full playlists, just audio, remove ads, and pretty much whatever functionality you would want for a program that downloads videos.

The program is still going strong today, with over 100,000 stars on GitHub, 7,400 forks, and extremely clear (and easy) download and usage instructions. Google has known about youtube-dl for decades, yet has take no action against the developers besides minimally rate-limiting downloads from the program.

Why would Google want to take down youtube-dl?
Why does Google continue let youtube-dl exist?

Google walks the same fine line with AdBlock Plus on Chrome.