Radio producer Dirk Maggs had consulted with Adams, first in 1993, and later in 1997 and 2000 about creating a third radio series, based on the third novel in the Hitchhiker's series. They also discussed the possibilities of radio adaptations of the final two novels in the five-book "trilogy". As with the film, this project was realised only after Adams's death. The third series, The Tertiary Phase, was broadcast on BBC Radio 4 in September 2004 and was subsequently released on audio CD. With the aid of a recording of his reading of Life, the Universe and Everything and editing, Adams can be heard playing the part of Agrajag posthumously. So Long, and Thanks for All the Fish and Mostly Harmless made up the fourth and fifth radio series, respectively (on radio they were titled The Quandary Phase and The Quintessential Phase) and these were broadcast in May and June 2005, and also subsequently released on Audio CD. The last episode in the last series (with a new, "more upbeat" ending) concluded with, "The very final episode of The Hitchhiker's Guide to the Galaxy by Douglas Adams is affectionately dedicated to its author."
Adams and Mark Carwardine contributed the 'Meeting a Gorilla' passage from Last Chance to See to the book The Great Ape Project. This book, edited by Paola Cavalieri and Peter Singer, launched a wider-scale project in 1993, which calls for the extension of moral equality to include all great apes, human and non-human.
Adams used email to correspond with Steve Meretzky in the early 1980s, during their collaboration on Infocom's version of The Hitchhiker's Guide to the Galaxy. While living in New Mexico in 1993 he set up another e-mail address and began posting to his own USENET newsgroup, alt.fan.douglas-adams, and occasionally, when his computer was acting up, to the comp.sys.mac hierarchy. Challenges to the authenticity of his messages later led Adams to set up a message forum on his own website to avoid the issue. In 1996, Adams was a keynote speaker at the Microsoft Professional Developers Conference (PDC) where he described the personal computer as being a modelling device. The video of his keynote speech is archived on Channel 9. Adams was also a keynote speaker for the April 2001 Embedded Systems Conference in San Francisco, one of the major technical conferences on embedded system engineering.