CLEO Library
CLEO Library is a custom tool developed to extend the scripting capabilities of GTA San Andreas.
The vanilla game has scripts that control the gameplay. They can be found in a binary file called main.scm. Editing game scripts is possible and many authors do so for larger mods, but it's far from being beginner-friendly. Any time you change main.scm you have to start a new game. main.scm has a very specific structure and the process of adding new scripts there is convoluted.
Here is where CLEO comes to the rescue. Managing CLEO scripts is much easier. Each script is a separate file, usually with .cs extension. To make the game aware of it, you just need to copy this file into the CLEO folder, which can be found in the game's root folder after you install CLEO Library. CLEO finds all .cs files in this folder and runs them automatically. You don't have to start a new game when you add a new CLEO script.
Removing a CLEO script is as easy as deleting its file from the CLEO folder.
CLEO Library can be found on the official website: https://cleo.li.