Portal

Portal is a mix between a computer novel and an interactive game. It was published for the Amiga in 1986 byActivision, written by Rob Swigart, produced by Brad Fregger and programmed by Nexa Corporation. Versions for the Macintosh, Commodore 64, Apple II, and the IBM PC were later released. A unique game for its time,Portal was one part text-driven adventure (à la Zork or Planetfall) but with a graphical interface.

The player, taking on the role of the unnamed astronaut protagonist, returns from a failed 100 year voyage to 61 Cygni to find the Earth devoid of humans. Cars are rusted and covered with moss, the streets are completely barren and everything appears as though the entire human race had just vanished suddenly. The player happens upon a barely functioning computer terminal that is tied into a storytelling mainframe, Homer. Through this interface, the player, assisted by Homer who attempts to weave the information into a coherent narrative, discovers information in order to piece together the occurrences leading to the disappearance of the human race. For instance, spending some time in the Medical Records section may unlock a piece of data in the Science section, and through these links the player can finish the game.

A hardcover novel, titled Portal: A Dataspace Retrieval and composed mostly of the text from the interactive novel with some new additions, was written by the same author, Rob Swigart and first published by St. Martin's Press in 1988. It takes the form of a series of notes on different subjects, in an order that the player would encounter them through Homer. A softcover edition was released by Backinprint.com in 2001.</p>

Now an ebook version has been released "under the Creative Commons BY-NC-ND Unported license 3.0" It has been authorized to be uploaded here by the author himself. http://67.205.70.12/forums/showthread.php?t=37197

(Source: Wikipedia entry)