Portable Application Description (PAD) is an XML format:
What is PAD? PAD is the Portable Application Description, and it helps authors provide product descriptions and specifications to online sources in a standard way, using a standard data format that will allow webmasters and program librarians to automate program listings. PAD saves time for both authors and webmasters. For more, see the PAD FAQ. 
Quoted from the Connected Flow Appcast page:
- Appcasting is the practice of using the 'enclosure' feature of RSS 2.0 feeds to deliver updates and release notes for new software applications.
Appcast + Sparkle
Sparkle, an application update framework, uses appcasts as described above, but adds several new features. An appcast with Sparkle extensions can, for example, have MD5 sums and DSA signatures.
DOAP (Description Of A Project) is a way of describing open-source projects. It has a
file-release property which can be used for describing application updates.