PHP Composer

It's an amazing tool. Simplifies dependencies management for PHP projects.
After really simple installation or setup you just define dependencies in JSON format in composer.json file like this..

{
  "repositories": [
    {
      "type": "pear",
      "url": "pear.php.net"
    }
  ],
  "require": {
    "doctrine/orm": "*",
    "symfony/yaml": "*",
    "pear-pear/Log": "*",
    "smarty/smarty" : "3.1.17"
  }
}

.. and run the command composer install. Or composer update if dependencies list updated. It creates a folder named vendor and all you project dependencies are there. You just have to include vendor/autoload.php and start coding.

If you still do not use it, I really recommend it.

Homepage can be found here.