Is there a good replacement for SaveTube?

I used to use SaveTube to download the audio portion of YouTube videos, ending up with an mp3 file on my computer (laptop).
However, I think that the SaveTube site has gone out of business. So, what is a good, safe replacement for it? By “safe”, I mean I don’t want to end up getting a ton of spam emails, or worse, viruses. If I have to look at a couple of ads, that’s OK.
I know that YouTube itself offers the capability to download not only the audio but the video as well, but I have to pay for it.
I’m looking for a free solution, because I’ll need to use this only once in while. I don’t need a subscription.