The Star Wars and Star Trek universes have spawned lots of novels that explore the characters and worlds. Some other sf/fantasy series have novel tie-ins as well.
Has any book series ever had this sort of official line of novels?
The closest I can think of is the Nancy Drew or Hardy Boys novels, but they weren’t openly written by various authors.
After exploring some of the fan fiction for Harry Potter in particular, it makes me wonder if Rowling could license the HP world/characters for offshoot novels. Has it been done?
Not only have series of novels based on characters been done but many argue that it is so overdone as to be destroying the field of f&sf (because talented newcomers find it more profitable to crack out a quick tie-in “tied” to a bigger name than to take the time to create a career based on their own original works).
You can find dozens of examples of big-name authors (or their heirs and estates) licensing others to create books in their universes: Isaac Asimov and Roger Zelazny are two that jump to mind.
There are even more books in which the big name lends a name to work that may be a true collaboration or more likely a book written from notes or an outline or nothing at all. Anne McCaffrey and Andre Norton’s collaborations are examples.
Baen Books likes to take its new authors and have them collaborate with bigger sellers to get their names out into the public. These will usually be in original series but may be related to or offshoots of ongoing series.
This is true in the mystery world as well. Both the Nero Wolfe and James Bond characters were continued by other authors. And of course there are orders of magnitude more Sherlock Holmes stories today than Conan Doyle ever wrote.
My guess is that there are hundreds if not thousands of examples of books based on print book series.
It’s simply way too early for Rowling to think of this and she is likely to deny others to play in her very personal world. But never say never. There were plans recently to continue C. S. Lewis’ Narnia series so who knows what might happen after she dies?
David Weber’s Honorverse seems to be a good example of this. There are the ten or so main books that he wrote centering around the character of Honor Harrington, a series of short-story anthologies with stories written by various authors, usually centering around either minor characters or characters newly made for the stories, and now there are some spinoff books based around different sets of characters. I don’t mind the spinoffing so much since many of the spinoff authors in this case seem to be better writers than Weber (it could also be that short stories are much easier to write than books, who knows).
Here’s hoping that many of these guys get their own series going too.
One of the Babylon 5 movies (Thirdspace) was aparantly inspired heavily by HP Lovecraft. It was also probably the best standalone movie from the B5 series.
Eric Flint wrote a novel 1632 about a modern town in West Virginia being sent back to 17th Centruy Germany. The book was originally intended to stand alone but proved to be very popular. So Flint co-wrote some sequels with other professional writers (mainly David Weber). But he has also encouraged fans to contribute. He maintains a website for fan fiction and some of the work from there has been published.