Pheeder XML Reader for Mac

From Pheed.com:

An extensible Macintosh desktop news and XML reader. Support for RSS, Atom, OPML, and various e-texts is built in. Users can define XSLT and plug-ins allowing Pheeder to work with XML feeds of any format. Tracks read items so you always know when something is new. Stay organized by arranging feeds in drag-and-drop folders. Auto-refresh feeds at user-definable time intervals. Set refreshing globally, for folders or individual feeds. Create dynamic search feeds that filter through your subscriptions and display only the items that match your search. View related Web site with an integrated, lightweight Web browser. Assign XSLT styles to individual documents. Ships with support for the various RSS formats, Atom, and OPML. Support arbitrary XML formats with simple plug-ins.