This just in from Terry Pratchett’s Twitter profile, a new Discworld novel by the name of Raising Steam is currently in the works.
There is some speculation as to whether this is the long-expected third book in the Moist von Lipwig character arc, which Pratchett had previously announced as being called Raising Taxes or if it features a completely new character, as other sources have reported.
The Wertzone author Adam Whitehead notes:
Pratchett had previously said that he was having difficulty making the tax-based book interesting. This is understandable, given that Making Money—Moist takes over the Ankh-Morpork Mint—was fairly close to being a retread of Going Postal—Moist takes over the Ankh-Morpork Postal Service—as it was. I would guess (and to stress this is guesswork) that Pratchett has taken Moist out of the tax office and put him in charge of the Undertaking, Ankh-Morpork’s under-construction subway system.