iCal is the program which Evolution uses to manage the calendar section.

Internet Calendar

Cal is a personal calendar application made by Apple Inc. that runs on the Mac OS X operating system. iCal was the first calendar application to offer support for multiple calendars and the ability to publish/subscribe calendars to Web DAV server.

Tcl by Sanjay Ghemawat for Unix systems. It is not related to the i Calendar format standard, and does not utilize it. It is also not related to Apple Computer's i Cal program.