FiveM is an alternate multiplayer service for GTA V. It is a modification for Grand Theft Auto V enabling you to play multiplayer on customized dedicated servers, powered by Cfx.re, along with possible mod support and a whole ton of stuff.
FiveM allows servers to use custom cars, maps, weapons, and more dynamically. FiveM allows servers to keep the original game AI, so you’ll never be alone. You can also PvE! FiveM uses Rockstar’s network code with improvements, so you’ll have the best sync around. FiveM doesn’t modify your GTA V installation, so you can switch between GTA:O and FiveM without getting banned.