Xtank is a fairly old but reliable graphical game requiring multiple players and optimised for a local area network of X displays. It features fast update rates, assorted mazes, various vehicles, simple graphics, drone tanks, and team play. Different game styles are possible; straight combat, territorial expansion, maze races with and without weapons, and ultimate frisbee. The "north" development branch is James Cameron's modifications to the 1.3f version for use on 800x600 displays in a network of Linux based second-hand gaming workstations in a rural village.
Freeciv is a multiuser reimplementation for Unix/X of the famous Microprose game of Civilization. By default, the game is an improved Civ II, but this can be customized; modpacks for near-100% compatibility with Civ I and Civ II are included. Multiuser gameplay is real-time: in each turn, all human players move concurrently. The game is designed to remain fairly playable even on poor network connections. Freeciv can also be played on standalone machines, and its AI players are a good challenge for beginners. The source code comes with the server, two X clients, and non-X clients for MS Windows and Amiga. Freeciv is released under the GNU General Public License. It is maintained by an international team of coders and enthusiasts, and is easily one of the most fun and addictive network games out there.
Netrek is a 16-player two-dimensional graphical real-time battle simulation with a Star Trek theme. A game is divided into two teams of 8 players (or fewer), who dogfight each other and attempt to conquer each other's planets. Netrek is the probably the first video game which can accurately be described as a "sport". It has more in common with basketball than with arcade games or Quake. Its vast and expanding array of tactics and strategies allows for many different play styles; the best players are the ones who think fastest, not necessarily the ones who twitch most effectively.
BZFlag is a 3D, multiplayer, tank battle zone, capture the flag game that pits players against each other in a networked environment. It runs on Windows 95/98/NT/2000, Linux, MacOS 10.x, Irix, Solaris, and others. An OpenGL accelerator is highly recommended, but it is playable with 3D in software.
Plasma EBG is an empire building game with an isometric view. It runs in multiple resolutions with graphics being displayed better for higher resolutions; hence, lower resolutions do not suffer from being too large, etc. In the future several viewing engines will be available, such as EBG-opengl and EBG-2d. There is a separate module called EBG-dev which features the latest AI-development, as well as a separate server module.