In 1984 Douglas Adams and Steve Meretzky of Infocom launched a text game version of Adams' book, which The Times described as the best adventure ever seen on computer, and it became a best seller. If you're a fan of the text adventure game style or just fancy of bit of computer gaming nostalgia, then you might like it. Billed as a "20th Century Edition", a knowledge of the original book in the Hitchhiker series will help you get started and you will encounter many familiar characters and locations, but Adams described the game as "bearing as much relationship to the books as Rosencrantz and Guildenstern are Dead does to Hamlet".
As a result of a competition to help fill out some missing location and item illustrations, there are even two versions available to play. The gameplay is the same but both have different illustrations to go along with the storyline. The site has pretty good instructions on how to play the game and there's even a hints section if you get stuck, and you probably will given Adams' "consistent illogic".