Google Calendar is a free Internet calendar that lets you keep track of your own events and share your calendars with others. It's the ideal tool for managing personal and professional schedules. It is both simple to use and very powerful.
The Google Calendar Interface
On the left-hand side of the screen, there's a miniature month, so you can quickly jump to different sections of your calendar by clicking on a date. On the upper right corner, there are tabs to switch between day, week, month, the next four days, and agenda views. The main area shows the current view.
The top of the screen has links to other Google services you've registered for, so you could schedule an event and check the related spreadsheet in Google Docs & Spreadsheets or fire off a quick email from Gmail.