Google Calendar - Spend less time managing your day & more time enjoying it

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.

Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.

Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.