Since your question is effectively asking for recommendations, I'm not sure how much mileage you'll get on any SE site. Maybe Software Recommendations, possibly Web Apps? Alas, I'm unfamiliar with both, so check their rules.
Also, you should bear in mind that since downloading YouTube videos is... legally ambiguous, at the very least, it may not fly anywhere on SE, and might be disallowed on either of those sites for this reason alone; check their respective rules for specifics.
*See links below, I found questions on both sites asking about this very topic, see if those answer your question outright before asking another on those sites.
If SE won't allow it, it's possible that Reddit might be a good alternative, I'm sure there are some relevant subreddits that could be helpful to you.
Links of interest: