0.91 RSS Feed

This is the simplified RSS version released by Netscape, and also the version number of the simplified version championed by Dave Winer from Userland Software. The Netscape version was now called Rich Site Summary, this was no longer an RDF format, but was relatively easy to use. It remains the most common RSS variant.

1.0 RSS Feed

This is an open format by the RSS-DEV Working Group, again standing for RDF Site Summary. RSS 1.0 is an RDF format like RSS 0.90, but not fully compatible with it, since 1.0 is based on the final RDF 1.0 Recommendation.

2.0 RSS Feed

This has the internal version number 2.0. RSS 2.0.1 was proclaimed to be "frozen", but still updated shortly after release without changing the version number. RSS now stood for Really Simple Syndication. The major change in this version is an explicit extension mechanism using XML Namespaces.

ATOM 0.3 Feed

The relative benefits of Atom in comparison to the two RSS branches are a matter of debate within the Web-syndication community. Supporters of Atom claim that it improves on RSS by relying on standard XML features, by specifying a payload container that can handle many different kinds of content unambiguously, and by having a specification maintained by a recognised standards organisation. Critics of RSS claim that Atom unnecessarily introduces a third branch of syndication specifications, further confusing the marketplace.

OPML (Outline Processor Markup Language)

This is an XML format for outlines. Originally developed by Radio UserLand as a native file format for an outliner application, it has since been adopted for other uses, the most common being to exchange lists of RSS feeds between RSS aggregators.