The Atom Publishing Protocol is now a real web standard (RFC 4287).
APP is different from, but closely related to, the Atom Syndication Format which is an XML format used for web feeds and an alternative to RSS feeds. The Atom Publishing Protocol goes a step further than syndication and uses XML-formated requests over HTTP to manipulate Web resources. In other words, it’s not just for reading, it allows for creating, reading, updating and deleting (CRUD) resources over the web.
Those of you following the development of Ruby on Rails will recognize APP as being an example of a RESTful protocol. (The REST model is one of the new features of Rails.)
With it’s ability to edit data and support for arbitrary media resources, Atom becomes useful for web feeds, wikis, calendars, photo libraries, podcasts, video distribution, document management… even software distribution. You can publish anything to the world and the world can interact with it!
The days of complicated web services like SOAP and WSDL are behind us. Atom and REST are on the rise and I’m interested to see what developers do with them. For example, there’s been a lot of discussion recently about opening up closed social networks like Facebook (here, here, here and here). Atom/REST could allow a simple way to share information between social networks. An update to your profile or friend list on one social network could ripple out to all of your others using Atom.
A good place to start learning more about Atom is Atom Enabled.