Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Lightning Calendar - Organize your life — it’s about time!
GoGetter - GoGetter is a task management system based on David Allen’s ever so popular Getting Things Done...
GMinder - GMinder is an open source Windows System Tray app that pops up to remind you about Google Calendar events.
todoMini - Your web based TODO list.
Calendar Lock PEA - Calendar Lock PEA is an encrypted desktop calendar with a day, week and month view. The shown calendars are never stored unencrypted on your disk, but exist only in the RAM. Platform-independent, Open Source, no installation or registration required.