If you care for both your productivity and the environment, look no further:
Forest is the app for you. Avoiding distractions actually becomes a fun experience, as the application turns your working effort into a proper game. You begin with choosing your preferred tree, and while you are working blood, sweat, and tears, your tree grows along with the effort. One tree represents one successful session of undistracted work. And the more of these sessions, the bigger your forest grows. Disturbing a session results in a dying tree, which, of course, you want to avoid at all times. The Forest application team collaborates with the real-life tree-planting organization "Trees for the Future", and provides the organization with donations earned by your hard work in the app. By now, already more than 550.000 trees have been planted, which must certainly convince you of the fact that it works. Forest is available for iOS and Android, and as Firefox add-on.