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.
Njam is a full-featured cross-platform Pacman-like game that uses the SDL library. It features single and multiplayer modes (local or network), duel games where players compete against each other to get more points, cooperative games where players cooperate to finish as many levels as they can, and great music and sound effects. It includes customizable level skin, many different levels, and an integrated level editor.
KBall is a game of skill and reflexes suitable for all ages. The idea is to move a ball around the map without falling or running out of time, and getting the prizes, in order to reach the exit. The map has different traps, such as slides, pushers, jumps, falls, and walls, etc. Maps are viewed from top view, and the walls and player's ball are real-time rendered in beautiful 3D. There is a map editor available inside of the game, to make custom maps.
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.