Usenet

I went with Eweka as a provider, don't remember why.

You'll also need a program to handle the downloading. I think there's a few but the popular one seems to be SABnzbd. I am not sure if you need that with the *arrs though, since I don't use those, but someone who does may be able to elucidate. And finally if you're interested in the forum-esque newsgroups (likely not) you can access those through Thunderbird.