Varieties of News Readers
I think — provisionally — that there are three types of news readers. (Am I missing any?)
1. Casual Newspaper
This category includes Flipboard, Zite (sadly defunct), the upcoming Apple News, and others. These tend to have the richest user interfaces of all news readers, with lots of pictures, animations, and interesting layouts.
Typically you pick some categories that interest you and perhaps some sites. You may also add RSS feeds and you might have it pull links from your Twitter and Facebook feeds.
These tend to have significant server backends that not only read various feeds and sites but also assemble (via algorithms and curation) a set of articles personalized for each user.
These are casual because, as with an actual newspaper, there’s no expectation that you’ll read everything. These tend not to have unread counts, for instance.
2. Productivity App
This category includes apps like Reeder, NetNewsWire, Google Reader (now gone), Feedly, Fever, and others. Their user interface often resembles a Usenet reader or email app. These apps often have things like unread counts and power-user features such as extensive keyboard shortcuts.
These tend to be RSS readers specifically, though not necessarily entirely so.
They don’t always do anything about relevance or personalization — personalization is entirely in the hands of the user, who picks which feeds to read. Some do include relevance features, but in general these apps are for people who want the control in their own hands, who don’t trust algorithms or curators, who don’t want to miss something that might be important.
There are two subcategories of productivity apps: browser-based server apps and native apps. Interestingly, the native apps often provide syncing by connecting to a server app (which may be made by a developer who’s not the same as the native-app developer).
3. River of News
These are reverse-chronological streams with optional titles and a short amount of text — often just a summary or excerpt of the linked-to story. (See Dave Winer on What is a River of News aggregator?)
These are also somewhat casual in that there are generally no unread counts and there’s no pressure to read everything. You read by scrolling, and you scroll as far as you want to.
There are two subcategories: RSS (or RSS mostly) and social network feeds. Twitter and Facebook could both be considered news rivers. (The RSS variety came first by many years, of course.)
Rivers sometimes have relevance algorithms behind them — as with Facebook, for instance — and sometimes not. They may be stand-alone, without any form of syncing, or they might have giant server back-ends — or something in between.