According to Chapter 4 of Douglas Adams' The Hitchhiker's Guide to the Galaxy, Damogran is a remote planet, in "the opposite spiral arm of the Galaxy, five hundred thousand light-years from the star Sol," generally deserted because it "consists of nothing but middling to large desert islands separated by very pretty but annoyingly wide stretches of ocean." (Two of these islands are called "Easter Island" and "France," but the book assures us this is coincidental and not a reference to the Earth locations of the same names.) It was used for the secret construction and intended launch of the ship Heart of Gold, which ended up as the theft of the ship by Galactic President Zaphod Beeblebrox.
The planet is described as very beautiful and scenic, with locations such as France seeming to be "not so much ... an island in its own right as simply a means of defining the sweep and curve of a huge bay. This impression was heightened by the fact that the inner coastline of the crescent consisted almost entirely of steep cliffs." About the only other information given about the planet in the book is the existence of a species of Damogran Frond Crested Eagle which makes a papier-mache nest with a few pages of Zaphod's unused launching speech, despite the fact that the infants will not be able to break out of the nest. "The Damogran Frond Crested Eagle had heard of the notion of survival of the species but wanted no truck with it."
The planet of Damogran turns up as a location in the Hitchhiker's Adventure Game, in a section of the game where the player takes the part of Zaphod Beeblebrox. The planet is also shown in the Hitchhiker's Guide to the Galaxy movie, for the same part of the plot as in the book (but with less detail).
Numerous people have used "Damogran" as a username or named something after it. The most amusing, in my opinion, is "Damogran Apathetic Solutions," at damogran.org, an organization of "people who like hacking together interesting applications" but due to lack of time, "regularly come up with interesting ideas that end up falling by the wayside. If we were to develop a strong emotional commitment to each one of these failed and forgotten projects we'd go insane. So in this case a little bit of apathy proves to be a bit of an asset."
Adams, Douglas. The Hitchhiker's Guide to the Galaxy. London: Pan Books, 1979.