I've never used it, but I've often thought about getting this one:
https://secure.profantasy.com/products/cc3.asp
It's not free, but it looks like it could be powerful.
[edit: Apparently I lost half a sen
I looked it over. It's pretty pricey because it seems to require a lot of DLC to get the good stuff. It also seems focused on making highly detailed local maps. I am building my world from the macro to micro so I want a world map first.
I guess I should specify I'm trying to create a D&D setting that can in theory work for any edition though my favorite is 3.5 (no need to derail this topic discussing best edition please). I created an organic cosmology of the gods, and I created a wide array of myths that explains reality. For instances, characters level up through surviving hardships and defeating mighty foes because the nine gods overthrew their tyrannical progenitor in a great battle and gained a portion of his power. Since the Nine shaped the world, their struggle was imprinted on the world in a microcosm. The Dragons were the descendants of their surviving foot soldiers (who also gained power by defeating the progenitor god). Elves and Humans were created by all the Nine to rule the world, but most of the gods didn't like the compromises they had to make so they tried to make their own versions of perfect races working solo creating Dwarves, Gnomes, Orcs, etc.
I pretty much have everything I need to create a setting apart from the geography. Looks like I got a lot of things to try. Anyway my planned world is a cylinder, not a sphere. One advantage of a cylinder is I can make a world map on a 2D surface and not seriously distort size and shape like with a globe. I need a map that I make multiple detailed copies to show changes over time.
Also I wanted to experiment with a different plane system. If you walk off to the top of bottom of the "can" you would walk into the Void which is a realm of aggressive nothing. There is a Barrier between the Void and the material but it's not perfect. The Void wants to suck out life but it can generally only suck out heat (which is why it's colder near the poles). The Barrier between the Void weakens when the year gets closer to anniversary of when the gods overthrew their tyrannical progenitor and stronger after the anniversary creating the seasons.
In the First Age the world I'm going for a Pangea-like landmass. Then the Dragons had a big internecine war and a mad queen tried to harness a the elemental power of the planet against her enemies and accidentally released a rogue horde of elementals which decided attack everything in sight, especially each other, splitting the land mass into smaller continents (along areas where water and earth elementals fought). Lesser skirmishers created lakes, rivers, and underground aquifers Less common elemental fights created a few anomalies. Flying islands where air and earth elementals once fought. Fire and Earth to make Volcanoes. Fire and Water to create hot springs and geysers. Fire and air to create rains of fire (in place I'm creatively naming the Fire Plains). The elemental rampage was called the First Unmaking.
After the elementals wore themselves out, the gods created new mortals to replace the nearly wiped out Dragons. In the Second Age the Elves took over until they got bogged down in an internecine war and a mad king tried to harvest a piece of the dead progenitor god to make himself a god and accidentally punched a giant hole in the Barrier releasing a mini-Ice Age and a rampaging horde of Void demons. Landmasses were changed as titanic magics were used by or against the incarnate Demon Lords. Also terrain was altered by glaciers or Demon defoliation. The Demon rampage was called the Second Unmaking.
The Third Age is the Age of Humans. I'm not planning to throw in a Third Unmaking unless players characters get to epic level, but I would like to make historical maps to show borders between Human and demi-human nations changes, along with the wilderness.
To complicate matters, I want to make a start of the Third Age map and have the gods put three or four ethnic groups/races of Humans in disparate places and then I want to see them organically develop with semi-realistic principles based on my favorite non-fiction book,
Guns, Germs, and Steel.