For the Willow movie release in the 1980s, I wrote The Willow Sourcebook generic roleplaying supplement, published by Tor Books as part of a doomed slate of licensed tie-ins. The book presented statistics in a format "compatible with" AD&D without actually infringing copyright. Though it turned out pretty well as a book, I think The Willow Sourcebook sold about ten copies worldwide.
Interestingly, there are Willow fans to this day who think highly of my book, although I believe the later Chris Claremont novels made much of the sourcebook obsolete.