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.
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.
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.
Tass: Threaded Usenet newsreader, ancestor of Tin. Tin is the most popular Unix newsreader.
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.
W3news: A flexible CGI tool that implements a Usenet newsreader through HTML pages. GPL'ed. Has been tested on Linux.
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.