iCal is a personal calendar application for Mac OS X
iCal was first premiered at Macworld Expo on July 17, 2002, which is why its icon has that as the calendar date. (It changes to today's date when the application is running). It was initially developed under the code name "WhiteRabbit" off of Apple's Cupertino campus. It was initially released as a free download to Mac OS X 10.2 Jaguar users later that year. It is a single-window application, with a calendar in the main part of the window, and the ability to display multiple separate calendars, organized by color, at the same time. It also functioned as a simple alarm clock for your Mac, alerting you with a popup, sound, SMS message, sending an email, or running a preset application.
Prior to iCal, Apple bundled Palm Desktop software with every Macintosh. What made iCal stand out was its integration with iSync (announced at the same time), allowing you to synchronize your mobile phone, Palm PDA, or iPod with your iCal calendars. iCal also supported the vCal and WebDAV standards, allowing you to subscribe to other calendars or to publish your own on a .mac or WebDAV server or export as a vCal file. Apple also released a bunch of public calendars for users to subscribe to; holidays, movie release dates, etc. iCalShare.com was created by fans and was even cited by Apple as a success of their product.
iCal 1.5 was released for OS X 10.2 and became a part of OS X 10.3 Panther. It had some interface tweaks, such as the event inspector becoming a drawer instead of a separate window, offering a wider range of camera colors, and supporting different time zones on an event-by-event basis or setting a time zone for the entire application.
iCal 2.0 was released as part of Mac OS X 10.4 Tiger. It added a search field at the bottom of the window, and integrated with Spotlight to show events and To-Dos in the Spotlight search windows. It also let you create invitations integrated with the OS X Address Book, which would automatically update RSVPs and responses in the background. iCal 2.0 also had improved actions with Automator, a new scripting program built into OS X. It also displayed birthdays from the Address Book and had improved calendar printing options.
With Mac OS X 10.5 Leopard, Apple improved iCal as to compete with business-class applications like Microsoft Outlook and Lotus Domino. iCal 3.0 features group scheduling, allowing multiple users to edit the same calendar, using the CalDAV standard (also used by Mozilla Sunbird). OS X Server Leopard will also have an iCal server built in for this purpose. It also features better ties with OS X's Mail application, allowing you to create or view To-Dos from within Mail.
Handy tip: Drag Address Book cards onto iCal to automatically create an event with a person or group. Drag an iCal To Do item into the main calendar view to create a new event, or drag events into your To Do list.