RSS Formats

Resource Description Framework (RDF) - general method of modeling knowledge
Dublin Core - provides a simple and standardised set of conventions for describing things online in ways that make them easier to find
CDF - Channel Definition Format (CDF) is an XML standard used in conjunction with Microsoft Active Channel and Smart Offline Favorites technologies. Its use is to define a website's content and structure
XML-RPC - XML-RPC is a remote procedure call protocol which uses XML to encode its calls and HTTP as a transport mechanism
OPML - (Outline Processor Markup Language) 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.
ATOM - The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol (APP for short) is a simple HTTP-based protocol for creating and updating Web resources.
The development of Atom was motivated by the existence of many incompatible versions of the RSS syndication format