Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
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.