Chaos Tool Suite is one of the best API module to use. The module mainly provides API.

I've worked on ctools before to create multi-step form and show that in popup. This time I'm working on a project which has a Quiz in it which is built using ctools. The site was having a requirement of displaying Quiz form when user clicks on link from E-Mail.

So to display ctools modal on page load we've to add below jQuery Code:

  Drupal.ajax.prototype.moduleName = function() {
    var ajax = this;
    // Do not perform another ajax command if one is already in progress.
    if (ajax.ajaxing) {
      return false;
    }
    try {
      $.ajax(ajax.options);
    } catch (err) {
      alert('An error occurred while attempting to process ' + ajax.options.url);
      return false;
    }
    return false;
  };

  /**
   * Define a point to trigger our custom actions. e.g. on page load.
   */
  $(document).ready(function() {
    // Since we need to display the modal only if below setting is set.
    if (!$.isEmptyObject(Drupal.settings.moduleName)) {
      Drupal.ajax[$('a.quiz-button').attr('href')].moduleName();
    }
  });

.quiz-button is class of link for user to start the Quiz.

Reference: