RPG Maker (RM) is a tool for making games.

I only have experience in using RPG Maker XP, RPG Maker VX, RPG Maker VX Ace, and RPG Maker MV.

Games made by using RM are based on

XP RGSS
VX RGSS2
VA RGSS3
MV rpg_core.js

In most cases, when I say RGSS, I mean RGSS, RGSS2, and RGSS3. RGSS is in Ruby and rpg_core.js is in Javascript.

The scripts of a basic RGSS game look like

def start
  # some codes
end
def update
  # some codes
end

start
loop do
  update
  Input.update
  Graphics.update
end

The scripts of a basic rpg_core.js game look like

function start() {
    // some codes
}
function update() {
    // some codes
}

Graphics.initialize(816, 624, 'webgl');
Graphics.boxWidth = 816;
Graphics.boxHeight = 624;
WebAudio.initialize(false);
Input.initialize();
TouchInput.initialize();
var deltaTime = 1.0 / 60.0;
var accumulator = 0.0;
var currentTime;
window.scene = new Stage();
start();
function performUpdate() {
    Graphics.tickStart();
    var newTime = performance.now();
    if (currentTime === undefined) currentTime = newTime;
    var fTime = ((newTime - currentTime) / 1000).clamp(0, 0.25);
    currentTime = newTime;
    accumulator += fTime;
    while (accumulator >= deltaTime) {
        Input.update();
        TouchInput.update();
        update();
        accumulator -= deltaTime;
    }
    Graphics.render(window.scene);
    requestAnimationFrame(performUpdate);
    Graphics.tickEnd();
}
performUpdate();

There is a simple rpg_core.js game written by me which can be accessed here. You can look at its source code by using your browser.

RM also provides a lot of scripts serving as making RPG. There is a simple RPG built by me which can be accessed here.

The source codes of RGSS are secret, but those of rpg_core.js are not a secret and can be seen at its GitHub repo.