I've noticed several times, that merchants want to modify prestashop engine, to display product or category page as homepage of their store. In this short guide i want to show you how to achieve that. Tutorial below is based on prestashop 1.5 engine, but you can use it also in new 1.6 release. 

If you're looking for solution for prestashop 1.7.x or 8.x and newest you can find ready to use module here:

product page on shop's homepage

Modified homepage - product specification

Controller modification

All what we have to do in this case is a simple modification of PrestaShop core. You can use override, or modify original core file. I suggest to create overrides, but everything depends on you. So, let's go. Please open /controllers/front/IndexController.php file. This file is a controller for your prestashop homepage. By default contents of this file looks like:

class IndexControllerCore extends FrontController
{
	public $php_self = 'index';

	/**
	 * Assign template vars related to page content
	 * @see FrontController::initContent()
	 */
	public function initContent()
	{
		parent::initContent();

		$this->context->smarty->assign(array('HOOK_HOME' => Hook::exec('displayHome'), 
			'HOOK_HOME_TAB' => Hook::exec('displayHomeTab'),
			'HOOK_HOME_TAB_CONTENT' => Hook::exec('displayHomeTabContent')
		));
		$this->setTemplate(_PS_THEME_DIR_.'index.tpl');
	}
}

Step 1

We have to change it a little. I will describe changes step by step below. It's time to first step. We have to change class definition. Instead of 

class IndexControllerCore extends FrontController

use

class IndexControllerCore extends ProductController

Step 2

Now we have to create init() function, in this function we will define what product you want to display on homepage. In this case, we have to create new variable $_GET['id_product'], exactly as i show below:

public function init(){
    $_GET['id_product']=1;
    parent::init();
}

$_GET['id_product']=1; this variable is a definition of product that you want to display. Instead of 1 use product id numer you want to display. if you don't know how to get product id, read this guide: how to get product ID in prestashop?

paste code above right after:

public $php_self = 'index';

Step 3

Now it's time to modify initContent() function. We have to remove all unnecessary code there. Just replace original function with this one:

public function initContent()
{
     parent::initContent();
}

... and thats all :) now you will see product specification on your homepage.

Full code of modified controller

class IndexControllerCore extends ProductController
{
	public $php_self = 'index';

	/**
	 * Assign template vars related to page content
	 * @see FrontController::initContent()
	 */
     public function init(){
        $_GET['id_product']=1;
        parent::init();
     }
	public function initContent()
	{
		parent::initContent();
	}
}