Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Lightning Calendar - Organize your life — it’s about time!
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
GMinder - GMinder is an open source Windows System Tray app that pops up to remind you about Google Calendar events.
Things - Things is an easy to use task manager.