free shipping gateway for marketpress. written as a reply to http://premium.wpmudev.org/forums/topic/option-on-marketpress-pickup-free-no-shipping-charge#post-750523

mp-free-shipping.php

<?php
/*
MarketPress FREE Shipping Plugin
Author: Aristeides Stathopoulos
Version: 1.0
*/

class MP_Shipping_Free extends MP_Shipping_API {

  //private shipping method name. Lowercase alpha (a-z) and dashes (-) only please!
  var $plugin_name = 'frsh';

  //public name of your method, for lists and such.
  var $public_name = '';

  //set to true if you need to use the shipping_metabox() method to add per-product shipping options
  var $use_metabox = false;
    
    //set to true if you want to add per-product weight shipping field
    var $use_weight = true;

  /**
   * Runs when your class is instantiated. Use to setup your plugin instead of __construct()
   */
    function on_creation() {
    //declare here for translation
    $this->public_name = __('Free shipping', 'mp');
    }

  /**
   * Echo anything you want to add to the top of the shipping screen
   */
    function before_shipping_form($content) {
        return $content;
  }
  
  /**
   * Echo anything you want to add to the bottom of the shipping screen
   */
    function after_shipping_form($content) {
        return $content;
  }
  
  /**
   * Echo a table row with any extra shipping fields you need to add to the shipping checkout form
   */
    function extra_shipping_field($content) {
        return $content;
  }
  
  /**
   * Use this to process any additional field you may add. Use the $_POST global,
   *  and be sure to save it to both the cookie and usermeta if logged in.
   */
    function process_shipping_form() {

  }

    /**
   * Echo a settings meta box with whatever settings you need for you shipping module.
   *  Form field names should be prefixed with mp[shipping][plugin_name], like "mp[shipping][plugin_name][mysetting]".
   *  You can access saved settings via $settings array.
   */
    function shipping_settings_box($settings) {
  }

  /**
   * Filters posted data from your form. Do anything you need to the $settings['shipping']['plugin_name']
   *  array. Don't forget to return!
   */
    function process_shipping_settings($settings) {

    return $settings;
  }

  /**
   * Echo any per-product shipping fields you need to add to the product edit screen shipping metabox
   *
   * @param array $shipping_meta, the contents of the post meta. Use to retrieve any previously saved product meta
   * @param array $settings, access saved settings via $settings array.
   */
    function shipping_metabox($shipping_meta, $settings) {

  }

  /**
   * Save any per-product shipping fields from the shipping metabox using update_post_meta
   *
   * @param array $shipping_meta, save anything from the $_POST global
   * return array $shipping_meta
   */
    function save_shipping_metabox($shipping_meta) {

    return $shipping_meta;
  }

  /**
* Use this function to return your calculated price as an integer or float
*
* @param int $price, always 0. Modify this and return
* @param float $total, cart total after any coupons and before tax
* @param array $cart, the contents of the shopping cart for advanced calculations
* @param string $address1
* @param string $address2
* @param string $city
* @param string $state, state/province/region
* @param string $zip, postal code
* @param string $country, ISO 3166-1 alpha-2 country code
* @param string $selected_option, if a calculated shipping module, passes the currently selected sub shipping option if set
*
* return float $price
*/
function calculate_shipping($price, $total, $cart, $address1, $address2, $city, $state, $zip, $country, $selected_option) {
    return 0;
  }

}

//register plugin - uncomment to register
mp_register_shipping_plugin( 'MP_Shipping_Free', 'frsh', __('Free shipping', 'mp') );
?>