I wasn't involved in this, but my friend Leia Tortoise was one of the editors and wrote the introduction; it was made in partnership with our website, the Vademecum - not that you'd know this from the promotional materials
It's official, but definitely an amateur endeavour, possibly print-on-demand for the French version; I have no idea about the commercial availability of the English translation (for all I know it was made only for Terry himself). It's not fanfic, mind you; only a collection of short stories that feature some kind of Grim Reaper figure. I only read Marie Devigne's story, as Leia lent me a copy for about five minutes and Marie is a Vademecum member; I'm very sorry to say that I saw nothing remarkable about it
Anthelme Hauchecorne's and Anthony Boulanger's are probably worth a read as they're both slightly well-known in the world of French SFFF amateur short story writers and have had multiple stories published before. This critic
read the whole book; she says there are some nice interesting ideas in there, but regrets that the stories don't live up to them due to their shortness and the writers' lack of experience ; but she liked Anthelme's longer story.
I personally think Paul Kidby's cover is the main draw of the book