I have an android app that [url removed, login to view]% completed. I'm having an issue with a calendar like function. In short a user has activities they can add to their account and are reminded every x amount of days / months / weeks. What you would have to do is ensure the reminders are sent out (I have some of the php code but it's not working), and when the user marks the event as "completed", the reminder goes away until next time.
Again all of the code is already written, it's simply not working 100%. With the reminders I'm using google cloud messenger and currently we are already storing the device id so we can send the message to the correct user, I beleive CRON is not running the service that gets the info we need to send out the message.