0verkill is a client-server 2D deathmatch-like game in ASCII art. It supports free connecting/disconnecting during the game, and runs well on modem lines. Graphics are in 16-color ASCII art with elaborate hero animations. 0verkill features 4 different weapons, grenades, invisibility, and armor. The package also contains reaperbot clients, a simple graphics editor, and a level editor.
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.
Heroes is similar to the "Tron" and "Nibbles" games of yore, but includes many graphical improvements and new game features including 12 original soundtracks, 94 levels (in 10 different tilesets), and five gaming modes including Quest (the classical Nibbles), or Kill'em all (squish the lemmings).
XPilot is a graphical multi-player maneuvering game with less-exciting graphics, but more speed, tactics, and insults. Some people also use it for UDP network analysis. Over the past eight years of playing and development, tons of features have been added to the game, from basic weapons like shotguns and missiles to more recent ones like phasing devices, invisibility, or hyperjump.
Vectoroids is based on the X-Window PDA game 'Agendaroids,' but uses libSDL for graphics, sound, and input, and includes nicer graphics, sound effects, and music. The objective is to survive wave after wave of giant rocks, which you must shoot to break into smaller pieces, until they are completely destroyed.
A220 Mission 1 is an arcade game written as a Java Midlet for cellphones. It lets you fly through mountains and cave systems, eliminating multiple enemies before finally destroying the Pirate Base. You pick up weapons, shields, and fuel powerups along the way. There are multiple levels, terrains, and enemies.
simpleJ emulates a simplified computer on your PC: a retro-style video game console that lets you understand how a computer works and write your own video game programs. The first microcomputers were quite simple. They had a few kilobytes of memory and couldn't run large programs. Many didn't even have an operating system. Yet they had something valuable: understanding everything about their hardware and software was easy. simpleJ aims to make this possible while running on modern PC hardware.