Reeder. It unfortunately syncs with Google, but otherwise, it's tops.

Really? Nothing in any screenshots suggest it can be set up this way.

Instead it looks like there's a list of synopses on the left which you must click to view a full story on the right?

I navigate without mousing:

https://homonculus.net/images/reeder.png

What Reeder shows on the left is the summary of the article; one can read the original by right arrowing. Many of my feeds put the full article into the summary. I navigate up and down the list (which is all of my feeds sorted by date ascending) with the j/k keys. I don't know how NNW does it. Or did it.

It sounds nice and all, but it's definitely not a River of News style reader.

RoN style is one pane, all of the stories from all feeds laid out, newest to oldest, in one pane, and you just scroll through them reading when something looks interesting. Think the way planet aggregators work.

Got it. I'd like that, actually. I approximate it now, but I'm not concerned with the feeds themselves, just the new items. Hmm.

There's an actual app called River of News for the iPad that does it quite well, but no Mac version, sadly.

NNW can be configured to work this way, but it's a bit clunky. Everything else I've seen seems to go with a standard Mail-type setup.