This free standalone multiplayer deathmatch game has a retro sci-fi look to it. The game takes place in the distant future as a war rages between big-brained Martians and Robots. It uses the GNU General Public License of the id Tech 2 engine. There is also single player through the use of configurable bots. The first release featured 5 player characters, 10 levels, and 9 weapons (both of alien and human nature). It featured vertex lighting on models, textured particles, stainmaps, and hi-res full color textures and skins. The HUD shows player deaths and high scorer at all times. All source code was released with game.
Version 2.0 added three brand new 1vs1 tourney levels, scripted shaders, quad and invulnerability shell effect added on weapon model and glass effects (helmets, tubes, etc) and intermission sequences were improved.
Version 3.0 offered 16 levels (3 new CTF), and several unique powerups, 9 player models and bots featured combat techniques such as rocket jumping, strafing, jumping and crouching. There was also CTF, Deathmatch, and Team Deathmatch rule options, shaders, scripted fog, and a new external browser/game launcher.
The final Version 4.0 had new CTF maps, improved bot AI, and all-new All Out Assault mode, in which players can hop into flying alien craft and battle one another. It also brought a Linux port and the now heavily modified engine is now called CRX and features new eye candy such as light blooms, multitexture combine, real-time dynamic vertex lighting, shaders, glass objects, reflective water, textured particle effects and much more.
Further versions starting with Alien Arena 2006 removed the "Code Red" reference and had the release year in the title.