OpenIV

Get the most recent version of OpenIV for free: You can view and modify game data with OpenIV, a free modding toolkit for Grand Theft Auto 5 and other games. You should only modify Grand Theft Auto 5 in offline mode due to limitations imposed by the game's publisher, Rockstar Games, or else you run the risk of being banned.

Mods for several games can be conveniently tracked in one location with this toolkit. Although modding games are becoming more and more popular worldwide, GTA5 Prison and Chaos Mod V are two options that are unique to GTA5.
https://openiv.org/