Folder notifications is a web app available on the Chrome Web Store and allow you to track change and new files added in a Google Drive Folder and in all sub folders too.
A free version of the app which allow to track one folder is also available to test it before buying a license.
This app has been published for the first time the October 6 of 2014 and last big update was made in January of 2015 to extend functionality and allow to choose time frame for notifications. This application is now used by 50% of Gmail users and 50% of Google Apps users.
For Google Apps users we have now users from 82 different companies who buy a license.
In terms of analytics, the number of notifications sent by week move from 300 to more than 1200 from January to May 2015.