This Symfony Form Experimental Branch example does not use the DIC.

form_definitions.php

<?php

class MyFormType extends AbstractFormType
{
    public function configure(FormBuilder $builder, array $options)
    {
        $builder->setDataClass("MyProject\FooEntity");
        $builder->add('my.sub_form');
        $builder->add('text', 'name', array('max_length' => 127, 'id' => 'foo'));
        $builder->add('date', 'created');
        $builder->add('choice', 'status', array(
            'expanded' => true,
            'multiple' => false,
            'choices' => array('active' => 'Active', 'inactive' => 'Inactive'),
        ));
        $builder->add('repeated', 'password', array('identifier' => 'password'));
        $builder->add('collection', 'stuff', array(
            'prototype' => 'my.sub_form',
        ));
    }
    
    public function getIdentifier()
    {
        return 'my.form';
    }
}

class MySubFormType extends AbstractFormType
{
    public function configure(FormBuilder $builder, array $options)
    {
        $builder->setDataClass("MyProject\BarEntity");
        $builder->add('entity', 'tags', array('class' => 'MyProject\Entity\Tag'));
    }
    
    public function getIdentifier()
    {
        return 'my.sub_form';
    }
}

form_example.php

<?php
/** Example to use without Symfony Dependency Injection Container */
// with DefaultFormFactory:
$factory = DefaultFormFactory::createDefault($validator, "csrfsecret", "storgesecrect", $em);
// or complex:
$factory = DefaultFormFactory::createInstance(new PhpTheme($templating, "path/to/theme_folder"), $csrfProvider, $validator, $tempStorage, $entityManager);
$factory->addType(new MyFormType());
$factory->addType(new MySubFormType());

// Usage
$factory->create('my.form');

form_experimental_type_creation.php

<?php
$factory = DefaultFormFactory::createDefault($validator, "csrfsecret", "storgesecrect", $em);
$form = $factory->createType(function($builder) {
    $builder->add('foo', 'text');
    $builder->add('bar', 'datetime');
    $builder->add('my.subform');
});

Its just an example i think :)