Crontab UI - Easy and safe way to manage your crontab file
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Scheduled tasks - GNOME GUI for configuring a users' cron (automatic jobs). Some of its features are:
GoGetter - GoGetter is a task management system based on David Allen’s ever so popular Getting Things Done...
024h Lucky Reminder - 024h Lucky Reminder is a reminder software for home and office.
todoMini - Your web based TODO list.