You can now download Terry Pratchett and Stephen Baxter's The Long Earth for only 1.99$ here.
Here's the blurb:
An unmissable milestone for fans of Sir Terry Pratchett: the first SF novel in over three decades in which the visionary inventor of Discworld has created a new universe of tantalizing possibilities—a series of parallel “Earths” with doorways leading to adventure, intrigue, excitement, and an escape into the furthest reaches of the imagination. The Long Earth, written with award-winning novelist Stephen Baxter, author of Stone Spring,Ark, and Floodwill, captivate science fiction fans of all stripes, readers of Kurt Vonnegut, Douglas Adams, and Carl Hiaasen, and anyone who enjoyed the Terry Pratchett/Neil Gaiman collaborationGood Omens. The Long Earth is an adventure of the highest order—and an unforgettable read.