Atom (standard)

Pivot

This is a validator for syndicated feeds. It works with RSS 0.90, 0.91, 0.92, 0.93, 0.94, 1.0, 1.1, and 2.0. It also validates Atom feeds. To use it, simply enter the address of your feed and click Validate.

Feedest intelligently learns what readers prefer, making constant adjustments to the ways of presenting the content provided by thousands of sources.

As updates and content flow in real time around the Web, conversations around the content are becoming increasingly fragmented into individual silos. Salmon aims to define a standard protocol for comments and annotations to swim upstream to original update sources -- and spawn more commentary in a virtuous cycle.

ebpage for changes.
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I mingle all your feeds into one to produce a combined RSS, Atom, JSON and a widget

an extension to the Atom feed format to express what people are doing around web

Atom is a simple way to read and write information on the web, allowing you to easily keep track of more sites in less time, and to seamlessly share your words and ideas by publishing to the web.

Republish your Blog or Feeds Without Coding
Choose your blog feed or one or more RSS, Atom or RDF feeds from the millions of already-published feeds.
Create a FeedSweep widget to display the
feed content in 1 minute or less. Sort, filter and customize to match your site's look and feel.

The Open Data Protocol (OData) is a web protocol for querying and updating data." Microsoft protocol built in part on AtomPub. Apparently occupies similar space to GData. Being made available under MS's Open Spec promise