A short story by Adams, "Young Zaphod Plays it Safe", first appeared in The Utterly Utterly Merry Comic Relief Christmas Book, a special large-print compilation of different stories and pictures that raised money for the new (at the time) Comic Relief charity in the UK. The story also appears in some of the omnibus editions of the trilogy, and in The Salmon of Doubt. There are two versions of this story, one of which is slightly more explicit in its political commentary.
A novel, Douglas Adams's Starship Titanic written by Terry Jones, is based on Adams's computer game of the same name, which in turn is based on an idea from Life, the Universe and Everything. The idea concerns a luxury passenger starship that suffers "spontaneous massive existence failure" on its maiden voyage.
Wowbagger the Infinitely Prolonged, a character from Life, the Universe and Everything, also appears in a short story by Adams titled "The Private Life of Genghis Khan" which appears in some early editions of The Salmon of Doubt.
Published radio scripts
Douglas Adams and Geoffrey Perkins collaborated on The Hitchhiker's Guide to the Galaxy: The Original Radio Scripts, first published in the United Kingdom and United States in 1985. A tenth-anniversary (of the script book publication) edition was printed in 1995, and a twenty-fifth-anniversary (of the first radio series broadcast) edition was printed in 2003.
The 2004 series was produced by Above The Title Productions and the scripts were published in July 2005, with production notes for each episode. This second radio script book is entitled The Hitchhiker's Guide to the Galaxy Radio Scripts: The Tertiary, Quandary and Quintessential Phases. Douglas Adams gets the primary writer's credit (as he wrote the original novels), and there is a foreword by Simon Jones, introductions by the producer and the director, and other introductory notes from other members of the cast.