Talislanta the setting is named for the continent which is its central focus. Though other, semi-legendary lands are mentioned in passing, The Chronicles of Talislanta (1987) makes a pitch for dropping the continent into any fantasy setting:
As to the land of Talislanta: those scholars who do not dismiss the topic out of hand disagree as to the origins of this otherwise forgotten realm. Some claim that Talislanta existed long ago, perhaps during the legendary First Age of Atlantis. Others, lending even broader scope to their imaginations, cite Tamerlin’s chronicles as proof of the existence of parallel worlds or alternate realities. Proponents of the hollow earth theory, avid readers of Charles Fort, and others of similar bent may formulate even more intriguing explanations for the Talislantan texts.This vagueness regarding the wider world doesn't last. In 1988's Sorcerer's Guide, Talislanta's world is placed on the plane of Primus within the wider Omniverse, not utterly unlike D&D's planar setup, but much less complicated. With the 2nd edition and The Talislanta Worldbook (1990), Talislanta's planet gets a name: Archaeus. Archaeus has seven continents in total:
The origin of magic in the Talislantan milieu is revealed for the first time. A tribe of "Sub-Men" (Talislanta's name for the primitive humanoid inhabitants of much of the continent) discover the wreckage of a ship of some kind and find a crystal orb that contains "the secrets of a lost and forgotten art—magic." Learning magic, these Sub-Men develop into the race known as the Archaeans (simply called "Men" in the 1st edition).
The 3rd edition largely follows the Worldbook's details, but demotes Archaeus from the center of its system to being a planet orbiting binary stars. This star system is just one of many within the material plane. The Sub-Men tribe uplifted by magic from a wrecked "strange vessel," now become known as Archaens.
Archaeus' solar system is de-emphasized in the last two editions, but the origin of the Archaens is now firmly established. In the 4th edition, Sub-Men is a derogatory term for the "Wild Folk" and the crashed ship is called out as "alien" and called an "ark." The 5th edition, affirms the ship was alien and states that it is believed to be of extra-dimensional origin. There are parts of it still in existence, recognizable by the rainbow color they emanate. The Sub-Men are again Sub-Men.
Why does the stuff about the Archaens matter? Talislanta was established from the beginning as a post-apocalyptic setting with frequent references to a Great Disaster. The Archaens were not only the ancestors of the "human" races of Talislanta, but the source of most of its magic, and also (perhaps) the cause of the destruction of their own civilization.
The idea of magic, or at least the advanced practice of magic, being alien in origin is a nice little detail to me, and one I don't think Talislanta has ever explored to its fullest. There is a lot that could be done with that in a campaign.
The vacillation between extraplanetary aliens and extradimensional ones, seems to coincide with some ambivalence about whether Archaeus is a planet in a science fiction conception or a "world" in a fantasy conception. I like a view of "outer space" more metaphysical than strictly physical, like in Medieval cosmology or pulp fiction like Howard's "Tower of the Elephant" or Lovecraft's Dream-Quest of Unknown Kadath, for Talislanta. I favor a more fantastic Archaeus, as well. One where you could sail across an ocean and into another world, perhaps.
Those preferences are in general. For the Sword & Planet thing I'm planning, I'm go with a much more realistic world around a realistic star.