RSS
RSS is a family of XML file formats for web syndication used by news websites and weblogs. They are used to provide items containing short descriptions of web content together with a link to the full version of the content. This information is delivered as an XML file called RSS feed, webfeed, RSS stream, or RSS channel.
The acronym stands for one of the following standards:
Rich Site Summary (RSS 0.91)
RDF Site Summary (RSS 0.9 and 1.0)
Really Simple Syndication (RSS 2.0)
WikkaWiki uses RSS feeds to allow users to track changes committed to the wiki. External RSS feeds can also be embedded in a wiki page.
More on RSS:
RSS at WIkiPediaCategoryReference
Also, RecentlyCommented looks at *pages* that recently had a comment posted to them - it tracks pages rather than all comments; it's RecentComments (the recentcomments action) that looks at *all* recent comments.
An XSLT can convert an RSS feed to Atom quite easily. Last time I checked, you could execute a transform with PHP pretty easily.
As for embedded feeds, we will probably switch to another, more flexible parser like Magpie RSS.