We'll create fresh WordPress site with bbPress – Anonymous Subscriptions installed. You have 20 minutes to test the plugin after that site we'll be deleted.
This add-on plugin for bbPress will allow anonymous users to subscribe to topics and get email notifications when a new reply is posted. The notification email includes an unsubscribe link.
bbPress notifications will keep to go out to registered users, this plugin only extends the thing to anonymous posters as well!
See the project on GitHub.
Available in English, Italian, German, Norwegian, Ebrew, Serbian.