Portal

If you don't have the patience to read the story of Portal within the game interface, Portal was also published as a novel by Rob Swigart. There was a U.S. hardcover edition from St. Martin's in 1988 (ISBN 0-312-01494-5) and a U.K. paperback edition from Grafton in 1989 (ISBN 0-586-20649-3).

The novel uses the game's format of presenting the story as short fragments "written" by Homer, supplemented by information from other databases. I haven't compared in great detail, but the text appears to be mostly unchanged from the game.