Added Custom Post Type Support

I added custom post type support to this plugin.

Edit the ical-feeds.php
1) after this line:
echo '<p id="categoriesUrl" style="display: none;">'.__('URL:', ICALFEEDS_TEXTDOMAIN).' <a href="'.site_url().'/?ical&category=" data-baseUrl="'.site_url().'/?ical&category=" target="_blank">'.site_url().'/?ical&category=</a></p>';

add this:

echo '<h2>'.__('Post Type iCal feeds', ICALFEEDS_TEXTDOMAIN).'</h2>';

    echo '<ul>';
    $args = array(
      'public'   => true,
      '_builtin' => false
    );

    $post_types = get_post_types($args);

    foreach ($post_types as $post_type) {

        echo '<li><a href="'.site_url().'/?ical&posttype='.$post_type.'" target="_blank">'.site_url().'/?ical&posttype='.$post_type.'</a> — '.__('Public iCal feed for', ICALFEEDS_TEXTDOMAIN).' '.$post_type.'</li>';

    }

	echo '</ul>';

2) after this line:
if (!isset($options['icalfeeds_minutes'])) $options['icalfeeds_minutes'] = 60;

add this:

$post_type = 'post';
    if (isset($_GET['posttype'])) {
          $post_type = $_GET['posttype'];
    }

3) replace both of the quires with this:

// Get posts

    if (isset($_GET['category'])) {

	    $posts = $wpdb->get_results("SELECT $wpdb->posts.ID, $wpdb->posts.post_content, UNIX_TIMESTAMP($wpdb->posts.post_date) AS post_date, $wpdb->posts.post_title FROM $wpdb->posts
			LEFT JOIN $wpdb->term_relationships ON ($wpdb->posts.ID = $wpdb->term_relationships.object_id)
			LEFT JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id)
			WHERE (".$postCond.") AND $wpdb->posts.post_type = '$post_type' AND $wpdb->term_taxonomy.taxonomy = 'category' AND $wpdb->term_taxonomy.term_id IN (".implode(',', $categoryIds).")
			ORDER BY post_date DESC $limit");

    } else {

        $posts = $wpdb->get_results("SELECT $wpdb->posts.ID, $wpdb->posts.post_content, UNIX_TIMESTAMP($wpdb->posts.post_date) AS post_date, $wpdb->posts.post_title
            FROM $wpdb->posts
            WHERE (".$postCond.") AND $wpdb->posts.post_type = '$post_type'
            ORDER BY post_date DESC $limit");

    }

4) I also changed X-WR-CALDESC variable to:
X-WR-CALDESC:Posts from {$blog_name}

Hope this can be implemented in the core plugin.

https://www.ads-software.com/plugins/ical-feeds/