BlogBridge looks pretty interesting: an open source, cross platform RSS reader. Their visual tour shows off many of the innovative features.
And guess what? They’re hosted on GitHub: http://github.com/pitosalas/blogbridge
From the README:
BlogBridge the most powerful blog and feed reader. Are you an info-junky? Here’s a high end aggregator that runs on any platform and is free to boot. You gotta check it out.