Reminder Commander - Reminder manager that reminds you about important events in advance.
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
GoGetter - GoGetter is a task management system based on David Allen’s ever so popular Getting Things Done...
Scheduled tasks - GNOME GUI for configuring a users' cron (automatic jobs). Some of its features are:
todoMini - Your web based TODO list.
JIT Scheduler - JIT Scheduler is a task scheduler for Windows 95/98/ME/NT4/2000/XP/2003.