Remind allows you to remind yourself of upcoming events and appointments. Each reminder or alarm can consist of a message sent to standard output, or a program to be executed.
It also features: sophisticated date calculation, moon phases, sunrise/sunset, Hebrew calendar, alarms, PostScript output, tcl/tk front-end and proper handling of holidays.
Reminders can be created by the remind scripting language or by using the graphical frontend "tkremind", which is also included in this package.
Homepage: http://www.roaringpenguin.com/penguin/open_source_remind.php