Hack to ghost core: mount/add new apps/sites on your ghost server

Install ghost from source

First, you should know how to develop with ghost.

create a new react app under core/server folder

simple example

core/server$ mkdir newapp
core/server$ cd newapp
core/server/newapp$ 
Ghost/core/server/web/newapp$ ls
app.js  controller.js  index.js
Ghost/core/server/web/newapp$ cat index.js 
module.exports = require('./app');
Ghost/core/server/web/newapp$ cat app.js 
const express = require('express');
module.exports = function setupNewApp() {
    const newApp = express();
    newApp.get('*', require('./controller'));
    return newApp;
};
Ghost/core/server/web/newapp$ cat controller.js 
const path = require('path');

module.exports = function newAppController(req, res) {
    res.send('Welcome to new App!');
};

Add route for your new site/app

./core/server/app.js

    // Mount the  apps on the parentApp
  
    // ADMIN
    parentApp.use('/ghost', require('./admin')());

    // import new app/site
    parentApp.use('/newsite', require('./newapp')());
    
    // BLOG
    parentApp.use(require('./site')()); 

Notes

above are for ghost before 2.0 version.
for latest ghost, version 2.0,
The folder for new app should be "Ghost/core/server/web/newapp"
The hacked core js is Ghost/core/server/web/parent-app.js
The code for add route is same as above.

Work your new app

grunt dev
navigate to http://localhost:2368/newapp, you will get: