CAL

CAL (or Cal) has several different meanings relevant to Doctor Who.

In-universe
CAL is the computer core of The Library.

Behind the scenes
CAL Video was a pioneer in the British CGI industry.

As name
"Cal" (or its variations) was the name of several characters:
 * Cal MacNannovich was a Platform One guest in "The End of the World" and therefore also a comic character in the Doctor Who: Battles in Time comic strip's first story arc.
 * Chal was the leader of the Savages in the serial of the same name.