Full Reminder

Default reminder is rarely enough. You may miss it at a time it rings (and depending on your device, it may not be loud enough).

Fortunately, apReminder+ solves this problem. It may repeat alarm for several times, so you can be more sure to hear it, and it can gradually increase volume so that it doesn't bother anyone if you are on the meeting, but also that you may here it if it is in your pocket. Finally, it may auto-snooze, and try again later if you haven't heard it for the first time.

It is even freeware.