Implements hook_rule_condition_info - add condition to rules.

foo.module

<?php

/**
 * Implements hook_rules_condition_info()
 */
function foo_rules_condition_info() {
  return array(
    'foo_check' => array(
      'label' => t('Check foo condition'),
      'parameter' => array(
        'param' => array(
          'type' => 'list<text>',
          'label' => t('foo label'),
          'options list' => 'callback_function_to_return_options',
          'description' => t('The condition to check for.'),
          'restriction' => 'input',
        ),
      ),
      'base' => 'callback_function_to_validate',
      'group' => t('System'),
    ),
  );
}


/**
 * Condition implementation: Check if param and condition is equal or not.
 */
function callback_function_to_validate($param) {
  $current_value = get_current_value(); // get the current value to check against condition value.
  return in_array($current_value, $param);
}

function callback_function_to_return_options() {
  return array(1 => 'value1', 2 => 'value2', '3' => 'value3');
}