Summarize this article:

Zebraboss will send you a daily email containing a list of users who’ve unfollowed you. You’ll have to set up Zebraboss through a web browser.   You will receive an email once per day with a list of users who’ve unfollowed you. Follow the “unsubscribe” link in the email at any time to stop using the service.
Open a web browser. Navigate to http://www.zebraboss.com. Type your email address into the second box. Click Subscribe for the report.