Unison offers all the expected newsreader functionality: easy-to-navigate threaded discussions, the ability to ignore annoying posters, multiple signature management, and easy, Mail-like posting with spell checking and all the trimmings.

It also goes much further than any other Usenet client, starting with a unique four-view interface that lets you view and work with Usenet group content in four distinct styles: messages, files, images, or music. It lets you preview MP3 files directly off a Usenet server, view images in an elegant iPhoto-like thumbnail view, prioritize transfers with a flexible downloads manager, find Favorites quickly with a categorized column-view interface, smartly group files into metagroups (such as songs into albums), and show the download status in the dock.

Limitations: 15 day trial

Requirements:
OS X 10.5+
Intel