Quitter
marco.org/apps
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Quitter is a Mac app that automatically hides or quits apps after periods of inactivity, inspired by my Automatic Social Discipline method. It’s great for minimizing distraction from social apps like Twitter and Slack, news readers, or even your email app.