I have no idea how useful this is to most, but to me, I found it at least noteworthy. I noticed in the terminal, at least in bash, that hitting Tab-Tab will let you see all the commands you have available to you. As I was scanning through them, a few caught my eye, namely leave.
Pulling up the man leave page told me the very simple usage. Simply type:
% leave +hhmmwhich will set an alarm for that many hours and minutes from the current time. To use a fixed time, drop the + flag, and it will allow you to set the leave alarm to some time in the future. You are reminded at five and one minute intervals. Nice thing about it in OS X is it actually audibly beeps at you.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031211233045903