KOULES is a space action game, that you bump your enemies, the KOULES spheres, to death. Well, or the other way around.
Its an addictive game, you can play alone or with friends up to five for deathmatch or cooperative. For single player, it has 100 levels and 5 difficulty levels.
The game has 256-color mode in 640x480, monochrome, or black/white mode. It can also run a server and accept other players from clients. It can be played with keyboard, mouse, or joysticks.
The opening Star Wars crawl is interesting, so is the README and the official website. You may also want to read the Koules.FAQ.
KOULES was created by Jan Hubička in July, 1995, written in ANSI C with SVGAlib/X11, run on Unix-like or OS/2 Warp, under GPLv2, currently Debian version 1.4-23 (2015-05-02, post v1.4(1998-03-09)).