Office 365 Alerts add-in has the Reminders functionality
Office 365 Alerts add-in was expanded with a new reminders feature that allows users to create SharePoint Email Reminders about upcoming meetings, tasks and any other dates.
It's never been easier to create a SharePoint email reminder with powerful tools for message formatting. You can add pictures, links, change the text view and include any details from SharePoint list fields. Reminder can be sent to SharePoint users and external email addresses as well. Also, reminders for recurrent events are supported.
The updated Office 365 alerts and reminders add-in is already available for download. Now you can manage all your Office 365 alerts and reminders within a single solution.