Vienna is a very promising new free RSS reader for MacOS. It's got the typical 3-paned interface that you can set to three vertical panes or the more traditional "1 left, 2 stacked to the right" interface you see in things like mail.app or Outlook. It's a little rough around the edges, especially in the usability department (notably the lack of useful command keys) but it's small and fast and has two really great features. First, it's pretty simple to re-style the visual appearance of the feeds using html and css. Second, and even better, is its ability to create what it calls 'smart folders.' These are meta-feeds that are created by parsing the contents of all your feeds and creating a new feed based on a comprehensive set of filters. This is a feature I love in the Windows aggregator FeedDemon, and Vienna's implementation is superior. To give you an example of how this works, in FeedDemon I have a filter set that watches for any occurrence of a set of terms related to diabetes, and every day I look over the output it produces, allowing me to take in, at a glance, all the research that's been published on the subject in the medical journals, plus every mention across the 'blogosphere' and in the mainstream press, every day. The usefulness of this can't be overstated, and Vienna is one of the few RSS readers to add this feature--to my knowledge Netnewswire is the only other one on the Mac that has this. If you're on a Mac and have not paid for Netnewswire yet, Vienna is well worth checking out.