I actually have three homebrew worlds, each designed specifically for certain campaign ideas I had and all in various states of being unfinished. They are all also heavily based on video games and shows that I watched at the time of their creation, as I do steal shamelessly from the things I like.

One was a sort of steampunk setting in a world with very maliable reality, allowing for all sorts of psychic powers and wuxia-esque shenanigans. The thousand year old ruler of a world spanning empire had just disappeared after fighting off a powerful demon (which are actually reality-devouring parasites travelling from world to world in this cosmology), leading to her empire fracturing. It splittered into four seperate nations, each preparing for war, and the intended campaign was supposed to be about an elite airship crew in the days before and during that war.

One of the nations legalized the use of alchemy to create zombies from indebted workers, enslaving them until they worled off their debts. Another idolized people and animals who became partially unreal after close encounters with demons, gaining essentially superpowers in the process. (But often just dying horribly as they fail to exist properly.) Those two were probably the most interesting.


The second is a sci-fi setting in the far future, where after earth becomes uninhabitable due to warfare, the remainder of humanity relocates to a far-away planet and its four moons. However, once there, the people who settle on the moons are heavily exploited as their new homeworlds are strip-mined for resources. A lunar coalition is formed that is then overtaken by a radical and power-hungry leader, pushing humanity to the brink of another apocalyptic war that may wipe them out for good. The idea was for the players to be part of a neutral peacekeeping force trying to sabotage both sides and work towards a peaceful solution.

To complicate the matter, there also were alien artifacts that had been found on the moon, and which had caused the rise of psychic powers within humans. Gaining access to them and discovering the truth behind them was intended to be a big part of the accompanying campaign.

Spoiler: Spoilers for the players I intend to eventually run this for.
Show
Oh, and those alien artifacts are actually the avatars of ascended forms of humanity in parallel dimensions. The humanity of this world had actually achieved that already, but the goddess they created as a result went haywire since she was used to destroy rival species. And those other avatars wish to reawaken her so they can control her, and are manipulating everyone to achieve this.

I watched too much anime before writing that setting.


The third was a post-apocalyptic real word setting for Godbound, where a cosmic tried to take over the world in secret for use in a never-ending war against another entity, but the champion she created rebelled after learning their true purpose and ended up turning earth into a momster-riddled hellscape.

The PCs were going to be her new champions, trained by her to fight the rebel in the torn-apart ruins of modern day America. The goal was something of a sandbox, with the players ultimately free to make their own decisions. This one is the most unfinished, as it really only has the cosmology and background, with an end goal of being something like Fist of the North Star meets Sin & Punishment.


I really should polish up one of these and put it out on the worldbuilding forums sometime. The only issue is that they were created with specific campaigns in mind, so most of the material I have is focused on what I wanted in those specific campaigns, not exactly on building very coherent worlds.