Whilst the dispute went on the Original Dungeons & Dragons game and the Tom Moldvay Purple Basic Set and Light Blue Expert Set were all players had. Eventually the dispute was resolved and Frank Mentzer proceeded to produce the Companion, Masters and Immortals rules sets.
At this time Bruce Heard was given charge of the freelance writing team at TSR and also responsibility for the less popular (although I suggest only in the United States) Dungeons & Dragons. The major innovation was the release of the Gazetteer series which fleshed out a lot of the world that latterly was coined "Mystara" but till then had simply been "the Known World".
There followed "The Hollow World" by Aaron Allston which revealed that Mystara was a hollow world and ancient empires were preserved by the Immortals on the inner side of Mystara's surface.
In the pages of Dragon Magazine Bruce wrote the column "The Voyage of the Princess Ark" about an Alphatian Airship which travelled to previously unexplored regions of Mystara.
These writings were later expaned on in the box set The Champions of Mystara, Red Steel and The Savage Baronies. Eventually with "Wrath of the Immortals" removing the continent of Alphatia from the face of Mystara and depositing it inside as part of the Hollow World setting, we lost our hero.
With the advent of AD&D 2nd edition, Mystara was moved to that rules set, its players went off got jobs, married, had children but the world never went away even once Wizards of the Coast stopped supporting it and even once Hasbro bought out Wizards of the Coast and turned D&D into something unrecognisable from its libertarian origins into something more resembling warhammer.
Bruce tried to get permission from Hasbro to revisit the world of Mystara, but Hasbro would rather leave the IP locked away from its willing audience.
In World of Calidar some of the themes are revisited in a totally new world, where airships are once more at the heart of the game and there is once again a new world to be explored.
I was delighted to support the Kickstarter project; on page 25 my step daughter Olivia Evans is immortalised as Olyffia Efanas (although I had no creative control over her behaviour in the story!), an island to the north west of the great caldera bears the name Pearcelsus Island and in a future publication the Airship the Lady Karevana will carry a crew through the skies or maybe between the planets & moons of the Soltan Ephemeris, we shalll just have to wait and see...
In the mean time Thorfinn Tait, the cartographer of Caldar takes us on a trip around the great caldera.
And through the Soltan Ephemeris to explore the other planets and moons which share a sun with Calidar.
The World of Caldar is available as a pdf or soft or hardcover book from DriveThru RPG.
Bruce Heard's Blog
Thorfinn Tait, Cartographer to the Stars
The World of Calidar Facebook Chat Group
World of Calidar on the Piazza Forums