Knews  
   For Unix-like systems. A threaded newsreader with an X Window interface. Distributed under the GNU public license. Handles MIME, attachments, killfiles, and launches URLs by clicking.
   http://www.matematik.su.se/~kjj/

NewsX  
   Freeware distributed under the GNU public lisence for Unix. Provides the NNTP capabilities required for serving a small local news spool. Also suitable for exchanging news with supplemental news sources for full scale news servers.
   http://www.kvaleberg.com/newsx.html

Tass  
   Threaded Usenet newsreader, ancestor of Tin. Tin is the most popular Unix newsreader.
   http://www.skrenta.com/tass/

PAN  
   A multithreaded Usenet newsreader for GNOME, a GUI desktop for Unix systems. Features decoding of binaries, automatic grouping of multipart posts, filters and killfiles. Supports multiple servers, offline reading, e-mail or Usenet replies.
   http://www.superpimp.org/

trn: Threaded RN  
   A textbased newsreader for POSIX compliant systems. Under development. Developer is looking for programmers who would like to help with the development.
   http://trn.sourceforge.net/

X-apps FAQ: III. X-based News-readers  
   The comp.windows.x.apps FAQ portion listing several Usenet clients for X-Windows, a Unix system GUI.
   http://www.ee.ryerson.ca:8080/~elf/xapps/Q-III.html

getbinnews  
   A Linux newsreader developed in C using the GTK user interface. Intended for searching and downloading of binary files. Screenshots, download and bug reporting available at this site.
   http://www.getbinnews.com

W3news  
   A flexible CGI tool that implements a Usenet newsreader through HTML pages. GPL'ed. Has been tested on Linux.
   http://www.damtp.cam.ac.uk/user/kp229/w3news/