How can I add Google Tag Manager's code to my website? Is there any module to add some new things like Google Tag Manager's code to Drupal based website? for example you should install Google analytic module to add analytic to your site, is any equivalent for Google Tag Manager?
There is an officially released module (since early 2014): GoogleTagManager.


  Allow the non-technical stakeholders to manage the analytics for their website using the Google Tag Manager (GTM). This module allows you to trigger the insertion of tags and tracking systems onto the pages of the site.