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.
Kobo Deluxe is an enhanced version of Akira Higuchi's game XKobo. It adds sound, smoother animation, high resolution support, OpenGL acceleration (optional), an intuitive menu-driven user interface, joystick support, and other features. Kobo Deluxe uses SDL for graphics, sound, and input, which makes it possible to run the game on a very wide range of platforms.
asq is a simple frontend for MAME/emulator cabinets. It runs in a terminal window using curses, and pops up an optional screenshot window. It uses MAME/emulator keybindings so you can control your MAME cabinet using just your MAME controls. (In fact, this is where the name comes from--player 2 buttons 1, 2, and 3 are "asq".) It can also remap your games to use MAME keys. asq is meant for people who don't want to use a keyboard and have lots of games to manage.