Pester 1.1

Pester is a simple alarm clock and timer for Mac OS X.

Pester is a simple alarm clock and timer for Mac OS X. You can use it to remind you to catch the bus or attend an upcoming meeting.

It is modeled after xalarm in functionality—though not in interface design.
If you're looking for a simple-to-use alarm clock and reminder for your Mac, Pester should probably do good job.