An updated version of the Event Reminders Plugin that is compatible with Moodle 2.9 was released on September 5, 2015.
From Moodle.org:
This plugin will automatically send reminders for Moodle calendar events in a timely manner via Moodle message interface. This plugin allows users to control how they receive messages for each event types in Moodle calendar.
Check out this update to this useful plugin and let us know what you think in the comments below!