Calendar applications

Google Calendar is a fully featured online calendar with great Gmail integration. Mobile support is excellent and sharing is easy to do.

30 Boxes acts as a hub for all your activities. It is your calendar and integrates your blog, instant messaging and twitter.

SlimTimer allows you to easily track how much time you spend on a task. Based on this a report can be created, for example to create an invoice.

Yahoo! Calendar is one of the largest web based calendar services.