What is Appcasting?

Appcasting is the practice of using the 'enclosure' feature of RSS 2.0 feeds to deliver updates and release notes for new software applications. The name Appcasting is by analogy with Podcasting, which is the practice of delivering audio files as RSS 2.0 enclosures.

The idea is this: the developer publishes an RSS 2.0 feed, each item of which describes a new release of a particular software product. The items' descriptions may contain release notes or other information about what's new in this release.

How does Appcasting help the users?

When your users are using RSS aggregators which support the RSS 2.0 enclosure feature, it becomes trivial for them to keep up to date with your software releases. Aggregators such as NetNewsWire 2 support downloading of enclosed content right in the aggregator.

How do I set up an Appcast Feed?

It's easy. There's really nothing technologically new here beyond RSS 2.0 itself. All you have to do is create your feed and in each item include a line like:

<enclosure url="http://example.com/MyApp-1.2.dmg" length="1048576" type="application/octet-stream" />

In the example, the url attribute is the direct download URL for your app, length is the length of the file in bytes and type is the file's MIME type.

Are there any developer tools to help?

Andy Matuschack's Sparkle framework is a complete Software Update framework that uses Appcasts to update applications.

Are there any Appcast feeds I can subscribe to?

Yes! There used to be a list of appcast feeds here, but the list grew so long - thanks, mostly, to the popularity of Sparkle - that maintaining it is no longer practical.

Appcasts are now in products from Bare Bones Software, The Omni Group, Red Sweater Software and many, many others.