Vienna from Steve Palmer just rocks. It’s s freeware RSS/Atom newsreader for Mac OSX, and it does what a newsreader is supposed to do (read all reasonable formats, import from and export to OPML, search within your subscriptions,…) but it adds a killer feature: Smart Groups for creating customized and rule based views on the entries.
Here is a (non exhaustive) list of some rules Vienna lets you play with:
Subject (is/is not/contains/contains not/…)
Folder (is/is not/within a given folder/subfolder)
Author (is/is not/contains/…)
Link (is/is not/contains/…)
Text (is/is not/contains/…)
Smart Folders can be created via File – New Smart Folder – the interfaces resembles the one for creating Smart Playlists in iTunes, no surprises there. The only feature I miss, is an or operator for combining the rules for a Smart Folder, but overall Vienna is just fantastic, and really really fast.
[disclaimer: I’m from Vienna (Austria), so my judgement might be blurred.]