CLEO Redux is an experimental JavaScript runtime for classic GTA 3D games.

It brings a joy of enhancing the gameplay with countless mini-scripts that are easy to add and remove. Both players and developers can equally benefit from a flexible and secure environment it provides.     LINK

This is a compiler, editor extension, and debugger for the GTA3script language, which was the de facto language used by Rockstar North to code the mission scripts of the 3D Universe. 

The editor extension is a extension for VSCode, which is a lightweight, cross-platform, and extensible text editor (definitely not Visual Studio). Such extension provides syntax highlighting, auto-completion and documentation crawled from GTAModding and GTAG. This provides access to the compiler as well, so there's no need to touch the command line interface if you aren't familiar with that.   LINK    TUTORIAL      

Sanny Builder is a fast and powerful tool designed for the GTA 3D game series.

It includes a disassembler, permitting the end-user to transform the game scripts into text and a compiler to translate source code written in the custom language back into the binary form readable by the game. A convenient editor has a large number of useful functions such as syntax highlighting, error checking, advanced search tools, player coordinates reading, fast movement through code and much more.  LINK

MoonLoader is a modification for GTA: San Andreas that brings new ability to use Lua scripts made by mods creators. With Lua scripts you can change some game aspects, expand gameplay and add new features. MoonLoader provides to developers extensive functionality for modding, it includes all familiar capabilities that CLEO has, and also combines many new features that were not previously available together in any GTA: SA modding framework. It is still a young modification and hasn't yet spread widely, but there are some scripts already made, and it aims to become the complete modern CLEO replacement!.   LINK      ALTERNATIVE LINK