Google Calendar, previously code-named "CL2", is a free contact- and time-management web application offered by Google. It allows users to synchronize their Gmail contacts with a web-based calendar. It became available on April 13, 2006 and is currently in beta stages. While users are not required to have a Gmail account, they are required to have a free Google Account in order to use the software.
The interface of Google Calendar is similar to desktop calendar applications such as Microsoft Outlook or iCal on Mac OS X. The Ajax-driven interface enables users to view, add and even drag-and-drop events from one date to another without reloading the page. It sports a variety of view modes, such as the weekly, monthly and agenda views. Users can "quick add" calendar events by typing standard English phrases, such as "Dinner with Michael 7pm tomorrow". Users can also set the number of days to show in their custom view mode. All events in a Google Calendar can be commented on by its users.
Events are stored online, meaning that the calendar can be viewed from many locations. In the case of a user experiencing a hard drive failure, it also means that no data is lost. The application can import Microsoft Outlook calendar files (.csv) and iCalendar files (.ics, the de facto open calendaring file format), although at this stage only when the fields are all in U.S. format.[citation needed] Multiple calendars can be added and shared, allowing various levels of permissions for the users. This enables collaboration and sharing of schedules between groups or families. There are also general calendars available for importing into one's account which contain national holidays of various countries.