Glorantha first sprang from the fertile mind of Greg Stafford in 1966. As he discovered the details of this imaginary world, he kept adjusting its cosmology, magic, history, politics, and cultures. Other contributors got involved, and Glorantha became arguably the most thoroughly developed of all fantasy roleplaying settings.
Wizards of the Coast selected The Forgotten Realms as the default setting for D&D 5 in part because the world is so deep. Since the days of Advanced Dungeons & Dragons, Ed Greenwood’s fantasy world has been fleshed out in adventures, setting descriptions, and other supplements. Now that I’m getting back into D&D after a long hiatus, I decided to see how much Forgotten Realms material had been published prior to 5th edition. The short answer is: a lot (and I didn’t even delve into the novels, comics, board games, and video games).