Begun by COR Entertainment in 2004, the game combines a 1950s-era sci-fi atmosphere with gameplay similar to the Quake, Doom, and Unreal Tournament series.

While the game's content is proprietary freeware, prohibiting commercial re-sale, the CRX engine is open source.

In 2013 the assets license was loosened somewhat, which allowed the game package to be included in certain Linux distributions, such as Fedora, Debian and Ubuntu.

The game is powered by the Quake II-based CRX game engine, which has been rewritten to include support for such features as 32-bit high-resolution textures, 3D models used as architecture in maps, GLSL per-pixel lighting effects, parallax mapping, normal mapping, ragdoll physics using the Open Dynamics Engine, server-side antilag code, shaders (GLSL and rscript), textured particles, semi-true reflective water with per-pixel distortion shaders, reflective surfaces on entities, light bloom, real-time shadows, overbright bits, real-time vertex lighting, and other graphical effects, all of which can be turned on or off in the menu.

Alien Arena has been compared to Quake III and Unreal Tournament, and is considered one of the best free first-person shooters.

[9] On November 3, 2017 COR Entertainment released Alien Arena: Warriors of Mars on Steam for Windows and Linux platforms.