We have modified several popular news clients to support GroupLens. GNUS is the very capable newsreader that runs inside emacs. A good choice if you frequently use emacs on any platform. SLRN is a popular terminal-based newsreader that allows you to view subject headers and article bodies at the same time in a split screen. A good choice if you don't read your news from a GUI environment.
Tin is another portable terminal-based newsreader.
Tin is not as easy to use as SLRN, but is loaded with more features than you can count. However, you must continuously switch between article header mode and article body view. Tin has been tested on Solaris, SunOS, Linux, and Irix. WinVN is one of the most popular Microsoft Windows-based news clients. It might also work on Windows 3.1.