
Terry Pratchett, other than lending his name to this book, wasn't a part of it. No humor and dark reading. Mr. Baxter should have published it under his own name, he can write, just not to my liking. gmb 3/15/20
Celestial Matters by Richard Garfinkle has Ptolemaic cosmology and Aristotelian physics.
The Planiverse: Computer Contact with a Two-Dimensional World by A.K. Dewdney is sort of a modern take on the classic Flatland by Edwin Abbot, and manages to improve upon it considerably.
The Long Earth series by Terry Pratchett and Stephen Baxter posits an infinite set of parallel Earths that can be reached with a trivial but unorthodox electronic device. You have to travel to them incrementally, one sideways step