About
Quake III Arena is a 1999 first-person shooter developed by id Software, the third game in the Quake series, built around multiplayer combat rather than a story-driven single-player mode (its single-player mode is played against computer-controlled bots), with a soundtrack by Sonic Mayhem and Front Line Assembly's Bill Leeb. ioquake3 is an actively maintained, open-source baseline engine for playing Quake III Arena, Team Arena, and their mods, built on the GPLv2-released original engine source. It modernizes the engine with an SDL2 backend, OpenAL sound, native x86_64 support, Mumble-based VoIP, Ogg Vorbis support, PNG textures, HTTP/FTP download redirection, and a CMake build system, among many other additions, while running on Windows, Linux, and macOS. It also supports building standalone games that don't require the original Quake III data.
How it differs from the original
The engine source was released under the GPLv2, but not the original game data — playing retail Quake III Arena or Team Arena content still requires owning a copy of the original game files, and the original map editor and compiling tools aren't included (a modern replacement is suggested instead).
Getting started
Prebuilt binaries and installation help, including a dedicated player's guide and a sysadmin guide for running servers, are available on the project's website; it can also be compiled from source using CMake on Linux, Windows, macOS, or via Emscripten for the web.