Electric Pocket has announced a Mac version of its Nag reminder app (http://electricpocket.com/mac/), offering a way to give yourself a persistent reminder that something needs to be done.
You can set an alarm for important events. When the alarm time comes, Nag will sound its alarm — and will continue its nagging every minute until you acknowledge the alarm.
Nag requires Mac OS X 10.6 or later. It’s available worldwide exclusively through the Mac App Store in the Productivity category.