vCalendar is an industry standard format for exchanging scheduling and activity-recording information electronically. If someone sends you their week's schedule in a vCalendar attachment to an e-mail note, you can drag-and drop it (or otherwise move it) to a personal information manager (PIM) type of application program and integrate with or relate it to your own schedule. vCalendar was developed along with the vCard electronic business card specification.
Like vCard, vCalendar was developed by a consortium founded by Apple, AT&T, IBM, and Siemens. The specification was turned over to an industry group, the Internet Mail Consortium (IMC), in 1996. Like vCard, vCalendar requires that you have an application program that supports its use. In time, it's expected that most personal information manager programs on all computer software platforms will support vCard and vCalendar as a standard exchange format.