I've used Vienna for years. It's Open Source.

http://www.vienna-rss.com/

> Vienna is an RSS/Atom reader for Mac OS X, packed with powerful features that help you make sense of the flood of information that is distributed via these formats today. The Vienna Project is continuously being improved and updated, so keep up to date with current development on the forums.

>Vienna is an OS X-native Objective-C/Cocoa Open Source project published under the Apache License, Version 2.0. It was started by Steve Palmer (aka stevewpalmer, stevepa) and is currently in active development by Jeff Johnson (aka johnson1234 and jeff_johnson_dev) and Michael Ströck (aka mstroeck). Many others have contributed immensely to this project, for details please download the application and load its “Acknowledgements”.

>Companies which have supported the project include GitHub, SourceForge (who provide all our web-hosting) and Senza Limiti.