The problem in installing the dependencies without Composer is the autoloading system.

Composer use a homemade autoloader based on an array map, this is a de-facto standard.
But this autoloading system, “fortunally” in this case, is not PSR-4 compliant.

PSR-4 is the de-iure standard for autoload a class in PHP, so you can’t escape from autoloading. You must use one of them.

In this case, this brilliant PSR-4 autoloader is capable to be manually configured to autoload a VendorClass in a VendorNamespace anywhere in your code, as long as you require the custom autoload.php file early in your source code.

Let’s look at this example:
I have a legacy project who can’t and won’t use Composer never and never even if God allow this with a miracle. This project can be speed up in development with this fantastic package for command line scripts.
This is my project directory structure:

 - src
 - tests
 - vendor (not the Composer's one)

This package has this directory structure:

 - examples
 - src
   - Commando
 - tests

The only thing I need is the src folder. Placing this folder in my vendor folder would be fine. So my custom autoloader would be like this:

// Constants
$base_path = "path\to\my\project";
$autoloader_class="\vendor\MarcoConsiglio-Wichee\PSR-4-Autoloading\Psr4AutoloaderClass.php";
define("BASE_PATH", str_replace("\\", DIRECTORY_SEPARATOR, $base_path));

// Autoloader
require_once BASE_PATH.'\vendor\MarcoConsiglio-Wichee\PSR-4-Autoloading\Psr4AutoloaderClass.php';

// Init the autoloader.
$package = [
    "nategood\commando" => [
        "namespace" => "Commando",
        "path" => str_replace("\\", DIRECTORY_SEPARATOR, '\vendor\nategood\commando\src\Commando')
    ],
    "kevinlebrun\colors.php" => [
        "namespace" => "Colors",
        "path" => str_replace("\\", DIRECTORY_SEPARATOR, '\vendor\kevinlebrun\colors.php\src\Colors')
    ]
];

// Register namespaces.
$loader = new \PSR4\Psr4AutoloaderClass;
$loader->register();
                      // Namespace                                      // Path to source
$loader->addNamespace($package["nategood\commando"]["namespace"],       BASE_PATH.$package["nategood\commando"]["path"]);
$loader->addNamespace($package["nategood\commando"]["namespace"],       BASE_PATH.$package["nategood\commando"]["path"]."\Util");
$loader->addNamespace($package["kevinlebrun\colors.php"]["namespace"],  BASE_PATH.$package["kevinlebrun\colors.php"]["path"]);

Now I can use the command package anywhere in my project!

This solution allow you to:

• Easely and manually build your own custom autoloader (you only need to specify the VendorNamespace and the folder(s) where search for VendorClasses in the VendorNamespace.
• Freely organize your composer dependency anywhere in your project folder (and why not, outside it)
• Import a composer package as is in your project (either downloading locally with Composer or cloning the package repository) or a relevant part of it (i.e removing composer.json file or files that require the composer autoloader).

Cons:

• Manually build your custom autoloader means to work on every required dependency of your project (i hope not a lot).
• Mistakes in package source paths can be tedious and frustrating.
• Works only with PSR-4 compliant file names (i.e. can’t use a A.class.php file name)