The original, closed-source versions of the game still work for online multiplayer. Many users may prefer to use more recent, improved engines based on the source code release.
id Software launched a free-to-play browser-based port of Quake III titled Quake Live, that has since migrated to Steam and is no longer free-to-play. Most players have migrated to this service to continue playing, as it adds new features and game modes, and improves compatibility with newer systems.
While the original Quake III Arena point releases still work on modern systems, the release of the engine's source code has enabled the creation of additional variants that improve upon the game but are backwards compatible for multiplayer play. These versions do not support PunkBuster anti-cheat and thus cannot connect to servers using it, though very few still exist.
ioquake3 is a port of the engine to SDL to assist in multi-platform development of stand-alone mods for the Quake III engine. For improvements this port provides, see the Improvements section.
Spearmint is a fork of ioquake3 source port to support XInput controllers and split screen multiplayer up to 4 players.
The game does not automatically adjust the aspect ratio to match widescreen resolutions. Certain cvars may be set to fix this: