Android: Calendars may be helpful for keeping track of what’s going on when, but they’re not always the best at making sure you remember when you need to do something. Calendar Events Notifier beefs up those notifications.
The app watches for your calendar notifications and, when it picks one up, it will remind you periodically until it’s dismissed. Unlike typical notifications, it’s persistent so you can’t swipe it away (or lose it in an errant Clear All). It will also buzz your phone every so often until you intentionally dismiss it. The free version works for all your calendars, but you can unlock the Pro version for $2 to specify which calendar you need to be bugged about.