From Shared Resources, Your Personal History

"Now those who want to research their Danish heritage can send Mr. Lundin a family tree in a format called Gedcom (from genealogical data communications), and his software will search a collection of family trees from other contributors for shared ancestors and cousins. The Gedcom file format, originally developed by the Mormon Church, is the lingua franca of the genealogy community; it allows users to convey information about ancestors, their birth and death dates and other information. Mr. Lundin's software looks for the best matches with other Gedcom files. When it discovers that two people have ancestors in common, Mr. Lundin said, he writes to both of them."