Thank you for the welcome
In my post, I forgot to mention "two" more games:
The Colour of Magic
Producers: Delta 4
Publisher: Piranha Games
Discworld: The Colour of Magic
Producers: Blue Sphere Games
Publisher: Blue Sphere Games
Year: After (not sure) 2006
Producers: Perfect Entertainment (PC) and Teeny Weeny Games (PS)
Publisher: GT Interactive
Year: (PC) 1999 and (PS) 2000
One could look into the copyrights for the games and maybe take the rights back to the writer/family/franchise.
As the games are made, there could be a chance to upgrade/bug fix and sell them to cellphone market for a few £/$ each.
One could, at the same time, make an online/box adventure game based on for instance Going Postal. With some parts of PVE sequences, the whole game based on chapters and between chapters (that could be started at any time), one could add chat option for online players, some of the games from the book series and so on. Each chapter, could have multiple endings/options. Something like an NPC in game making same questions with a different tone: polite, joyful and rude. Answers from the player would have same tones, but each different choice, would give the player different attributes in the next game.
Next game based on for instance Hogfather, could be a digital/box MMORPG, based on similar principles as Guild Wars game. Where a player enters own versions of explorable parts of the game and towns where a player (as she/he levels) can get a glimpse of the next games. This game version will enable a player to follow a/multiple stories where one can learn more about the Discworld. Yet again, better "scores" in this game, would give better options in the next game in the series. In this part of the series, player would be introduced to a cash shop system that would be of help to max out the ending "scores".
The last game of the series based on for instance The Colour of Magic. Where the player follows in Rincewind tracks and explores deeper in to the different and more dangerous parts of the Discworld. In this part, player would meet the challenges of PvE and/or PvP and a more advanced game play/cash shop.
Just a few ideas that crossed my mind.
PS. I use the 3 stories, as there are movies already done and a lot of fan art is around. It also gives a chance to maybe have a better chance of "selling" the whole pacage: books, art, online/cellphone/board/card games, movies and any other item from Discworld brand name.