Remembering Role Aids
One of my more humorous moments explaining a gaming book occurred in the mid-1980s. I was in the back seat of my grandfather's car flipping through Role Aids' Elves book while we were stuck in traffic on Ocean Parkway in Brooklyn. My grandmother asked what I was reading and I showed her the book. She misunderstood the title and thought I was reading a book about Elvis, not Elves. To this day when I look at the cover of that book I keep thinking it does kinda look like he's getting ready to rock...
Since the 3rd edition of D&D Wizards of the Coast has embraced third party adventures, though they were perhaps a bit less receptive in the 4th edition era. They had made the discovery they made their most money on books that everybody bought - rulebooks and supplements. Adventures might be needed but they didn't make nearly as much money.
Prior to that, the original owners of D&D, TSR, was rather draconian about allowing 3rd party products. They did license miniature figures, but to the best of my recollection, they never allowed any official 3rd party products outside of Judges' Guild and actually worked rather hard against them, going so far as to institute rather draconian policies towards fan-made material in the early days of the internet. Mayfair Games' Role Aids is one of the few 3rd party lines I can think of from the TSR era. I know that Kenzer and Company had a pair of Kingdoms of Kalamar books and I remember a series of class books from Bard Games.
Back in the day I had quite a collection of Role Aids books. They had a bit of a dance renaming various stats to avoid running afoul of TSR's trademarks - Hits to Kill instead of Hit Points, Skill instead of Level, etc. They were unsuccessfully sued by TSR in 1993 and TSR eventually bought the line.
Like any other series, the books were of varying quality. Some of their books were straight out adventures (often loosely connected into a campaign) while others were longer books, serving as both sourcebooks and adventures. In the early 1990s they published some fantastic supplements on Demons that I made extensive use of in my gaming.
My favorite book from the Role Aids line would have to be their Wizards book, covering various wizards from legend and fiction, often with introductory sections written by the character's creator. This book introduced me to the works of Robert Lynn Asprin, Roger Zelazny, and Marion Zimmer Bradley, as well as making Babylonian mythology come alive with its section of Gilgamesh.