You’ve heard of the Chrome Web store and you’ve probably heard of the Drive App section of Google Drive. Well, now Google Docs and Sheets have their very own section for add-ons!
These tools, which are built on top of App Script, bring advanced functionality to Docs and Sheets that aren’t available natively. For example, you longer need to stress over creating a mail merge with Apps Script. The Merge tool brought to your by MailChimp should make that process much simpler from now on.
Check out the announcement on the Google Drive Google+ page for more information and an introductory video.