Hogwasher by Asar, Inc. does news and e-mail. "When is a 'free' newsreader not free? When it costs you money in download charges. Hogwasher is the only Mac newsreader to offer 'virtual servers': the ability to combine articles across multiple servers, thus saving you time and money. Hogwasher sets the standard for Mac newsreaders in both ease of use and power. Outlook Express users will appreciate it's optional multi-pane interface. And all users will appreciate it's email client and support of all common encodings including yEnc. OS X and Classic." If you use or have tried Version 4, let me know what you think of the text snippet feature!
Penelope "is an open source extension to the Mozilla Thunderbird mail application." (I believe it thus has all Thunderbird features, including nntp newsreader).
Osiris "A drag and drop application to post a folder or folders of files to specified newgroups using Thoth or MT-NewsWatcher. OS X only." Supports yenc encoding.
Nemo by Malcom mac software is a "Newsgroups/Usenet reader made for Mac OS X. You can follow your favourite discussion with an elegant and powerfull user-interface that is designed to look and behave like an Apple Application. It also uses the most recent Mac OS X technlogies like WebKit and Spotlight. Nemo is a native Cocoa Application available both in Intel and PPC platform (Universal Binary)."
Xnntp by F. Zschocke is a free, native COCOA, nntp-newsreader available for Mac OS X 10.3.9 and 10.4 with Spotlight integration. Currently in beta -- testers are needed.
NewsCarrier by Daniele aka Malcom. "The goal of this new app is to create a free-opensource complete newsreader designed around the best GUI experience ever made, Aqua."
Gone?
NewsFlash (sourceforge Open Source) "features a gorgeous non-blocking Aqua GUI married to an architecture which supports multiple NNTP news servers, multiple concurrent operations and true (by reference) article threading." No longer in development, but source is available.
OSXNews an online OS X (written for Cooca) by Anurodh Pokharel.
Pineapple News for Mac OS X by Allen Brunson. "Pineapple News is a USENET newsreader for Mac OS X. It is primarily an offline reader, but it has features and user interface conventions that make it easy to use online also. It uses the traditional three-pane paradigm. The program is easy to set up and use."