Google has launched a new tool that can come handy for corporate users.
The service also allows you to add third party code. You can even add non-JS code. Google is offering easier integration with their own services like Google Analytics.
The service is free and has some limitations. Google said:
Google Tag Manager is quick, intuitive, and designed to let marketers add or change tags whenever they want, while also giving their IT and webmaster colleagues confidence that the site is running smoothly—and loading quickly—so that your users are never left hanging.
Tags that are not supported yet:
Synchronously loading tags.
Certain tags with snippets in the header and the footer. While you can use event based rules on gtm.load to fire some of these tags, two-part tags usually imply some need for synchronously loading tags.
Tags that are associated with in-page structure, such as social sharing widgets or ad serving tags.