Having sold more than 70m books in his career as an author, Terry Pratchett is now turning his attention to the App Store. He's announced plans for an iPad app based on his Discworld books.

"You might think it's exciting news: a new Discworld app is coming," announced Pratchett in a 17-second teaser video posted on the app's official website. "It's secret, so keep it under your hat!"

A release date for the app hasn't been announced beyond the "Coming Soon" message at the end of the video. The publisher is Transworld Publishers, a subsidiary of Random House.

The company has been working on the app with British developer Agant, which has worked on a series of book-apps with publishers, most recently two Shakespeare apps for Cambridge University Press.

Managing director Dave Addey tweeted a link to the teaser website this morning, and received a warm response from peers in the apps industry. "From the responses to my last tweet, it would seem that quite a few of you are Discworld fans," wrote Addey afterwards. "More app info to follow in due course!"

The app's title indicates that it's a spin-off from Pratchett's Discworld books rather than a digital version of a specific novel. Its release is part of a wider trend for publishers to explore ways of bringing fiction to tablet devices.

One good example released as Pratchett's announcement was being made is War Horse, an iPad version of Michael Morpurgo's acclaimed novel, hot on the heels of its cinematic and theatrical success.

That app does present the novel, accompanied by an interactive timeline of First World War historical documents and video interviews, and an audio reading of the book by Morpurgo. It's also a collaboration, this time between the original book's publisher Egmont, apps publisher Touch Press, and film company Illuminations.

Another example of (adult) fiction books being turned into apps in 2012 is Random House's A Clockwork Orange, which complemented the text with the original 1961 typescript and audio clips of author Anthony Burgess and critics discussing the book.

Meanwhile, this week HarperCollins launched five enhanced e-books based on The Hobbit, capitalising on publicity around the upcoming film trilogy based on Tolkien's book.

The publisher worked with developer Yudu Media on The Visual Companion, The Official Movie Guide, The Official Annual, The World of Hobbits and The Movie Storybook, using Apple's iBooks platform to include interactive maps, puzzles and zoomable imagery.