CategoryAttribute.php

$this->startSetup();

/**
* Use those two commands to delete the attribute for testing
*/
//$this->removeAttribute('catalog_category', 'custom_attribute_1');
//$this->removeAttribute('catalog_category', 'custom_attribute_2');


// creating the attributes

$this->addAttribute('catalog_category', 'custom_attribute_1', array(
    'input'         => 'multiselect',
    'type'          => 'text',
    'label'         => 'Category Filters',
    'backend'		=> 'eav/entity_attribute_backend_array', // this is important so the system can undertsand to convert the options to a string to be saved
    'visible'       => true,
    'required'      => false,
    'visible_on_front' => true,
    'global'        => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
    'source'		=> 'Custom_Module_Model_Options', // you use this for custom option in your own class
    'position'      => 100,
    'group' 		=> 'Custom Attribute 1',
    'user_defined'	=> true,
));

$this->addAttribute('catalog_category', 'custom_attribute_2', array(
    'input'         => 'select',
    'type'          => 'int',
    'label'         => 'Category Filters Enabled',
    'backend'       => '',
    'visible'       => true,
    'required'      => false,
    'visible_on_front' => true,
    'global'        => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
    'source' 		=> 'eav/entity_attribute_source_boolean',
    'position'      => 99,
    'group' 		=> 'Custom Attribute 2',
    'user_defined'	=> true,
));
 
$this->endSetup();