Modules
https://www.drupal.org/project/danse
Framework for sending notifications.
https://www.drupal.org/project/message
A messaging framework, has much more use than danse.
Docs: https://www.drupal.org/node/2180145
https://www.drupal.org/project/message_digest
Email digests.
https://www.drupal.org/project/notify
Is this functionality covered by DANSE?
https://www.drupal.org/project/admin_content_notification
Is this functionality covered by DANSE?
https://www.drupal.org/project/entity_activity
Covered by message + flag.
https://www.drupal.org/project/simplenews
Robust newsletter framework.
https://www.drupal.org/project/mailing_list
Email subscription lists. Simplenews looks better.
https://www.drupal.org/project/notificationswidget
UI for notifications.
https://www.drupal.org/project/notify_widget
UI for notifications.
https://www.drupal.org/project/events_log_track
Log system events.
https://www.drupal.org/project/email_confirmer
Useful for confirming non account signups?
https://www.drupal.org/project/views_send
Send mass emails from views
https://www.drupal.org/project/user_mailman_register
Integration with Mailman (set up separately). Will not support mailman 3.
https://www.drupal.org/project/mass_contact
More for one off emails.
https://www.drupal.org/project/usernotification
Send emails to users, seems similar to mass contact.
https://www.drupal.org/project/user_update_notify
Notifications of user changes.
https://www.drupal.org/project/page_notifications
Subscribe to page without an account.
https://www.drupal.org/project/content_notify
Notify users of content changes. Covered by DANSE?
https://www.drupal.org/project/ckeditor_mentions_notifications
Tag users in comments and send messages!
https://www.drupal.org/project/push_notifications
Push notifications to mobile devices.
https://www.drupal.org/project/alert_message
Sitewide alerts.
https://www.drupal.org/project/notification_message
Sitewide alerts.
Recipe: https://www.drupal.org/project/alerts_format
https://www.drupal.org/project/alerts
Sitewide alerts.
https://www.drupal.org/project/conditional_notification
Send emails per entity.
https://www.drupal.org/project/permission_watch
Notifications about permission changes.
https://www.drupal.org/project/workflow_notifications
Notifications triggered by workflow changes.
https://www.drupal.org/project/webform_digests
Useful for receiving webform submissions.
https://www.drupal.org/project/custom_notifications
Seems less robust than DANSE or message.
https://www.drupal.org/project/email_notifications
Log sent emails and allow resending.
https://www.drupal.org/project/group_notifications
Notifications for groups. In development.
https://www.drupal.org/project/content_notification
Advanced version of Admin Content Notification
https://www.drupal.org/project/admin_notification
1 site using.
https://www.drupal.org/project/content_moderation_notifications
Notifications for moderation changes.
https://www.drupal.org/project/notification_update_nodes
Email when content is updated. In development.
https://www.drupal.org/project/calendar_event_notifications
Notification for calendar events.
https://www.drupal.org/project/web_push_notification
Browser push notifications. In development.
https://www.drupal.org/project/browser_push_notification
Browser push notifications. In development.
https://www.drupal.org/project/simple_content_notifications
Content update/needs review notifications.
https://www.drupal.org/project/inotify
Linux inotify integration. In development.
https://www.drupal.org/project/webhooks
External notifications/event triggering API.
https://www.drupal.org/project/group_notification
Group notifications.
https://www.drupal.org/project/commerce_stock_notifications
Commerce stock list notifications.
https://www.drupal.org/project/private_message
Send messages to users.
https://www.drupal.org/project/comment_notify
Notify when comments are made.
https://www.drupal.org/project/message_notify
Part of Message Stack.
https://www.drupal.org/project/message_subscribe
Part of message stack.
https://www.drupal.org/project/message_notification
How is this different than message_notify?
https://www.drupal.org/project/notification_popin
Instant notifications? Or just popups?
https://www.drupal.org/project/email_changelog
Track when user email changes.
https://www.drupal.org/project/entity_changelog
Track when entities are changed.
https://www.drupal.org/project/elogger
Track entity form submissions.
https://www.drupal.org/project/send_emails
Email sending API.
https://www.drupal.org/project/content_update_email_sending
Send emails when content is updated. In development.
https://www.drupal.org/project/mail_notify
Send emails when content is updated.
Documentation
Drupal newsletter module comparison
https://www.drupal.org/node/645108
Notifications via email comparison:
https://groups.drupal.org/node/15928