A while back, Matt Gemmell wrote a great little US$3.00 utility called Sticky Notifications that merged Mountain Lion's notification center with sticky notes. It allows you to pin reminders to your desktop.
Now, Jeremy Tregunna has released a time-triggered twist on the idea. His Scheduled Notifications utility lets you specify when you want to be pinged.
"I was using Sticky Notifications to remind myself to do a couple things at a time," he writes, "These were things which i didn't need to do now, but in 10 or 30 minutes. They were eating up space on my screen and covering my inspector panels in Xcode."
He wanted to be able to fire them up, but have them trigger at a specified time. So he got to work and put together a utility that would use real-world formatting (like "tomorrow at 5PM") and an easy-to-fill-out form.
The result is Scheduled Notifications ($2.99), which he will distribute both through his own site and, once he gets through Apple's hoops, the Mac App Store.
I gave the app a try and found it easy to use. You can schedule notifications and then preview what notifications are coming up. It does have a few quirks, as you would expect in an early release. For example, new notifications don't always show up properly in the upcoming (Command-U) list.
That said, it's a simple, friendly utility that many OS X Mountain Lions users will find helpful -- and being sold at a price that won't break the bank.