I've been thinking a lot about science fantasy lately, and how for me it hits a ton of buttons I enjoy. However, I've yet to find that 'perfect' science fantasy; there are some great games out there like Numenera and Rifts, but none hit my itch.
However, I've thought about a pretty easy solution: hacking Goblinoid Games' Mutant Future to be less post-apocalypse and more to its science fantasy ideals.
Mutant Future's main conceit is that the world was obliterated by warfare or whatever, and a few generations later it has returned to a medieval society. But what happens if this society continues into the future even farther, basing their technology on the Clarke's Third Law nature of MF?
In essence, a post-apocalyptic Eberron that shares a lot of ideals with JRPGs like Phantasy Star and Final Fantasy.
As I see it in my head, the pre-apocalyptic society didn't reach retro-futuristic atomic era tech, but rather borderline transhumanism tech. The biggest innovations of this era were basically cybertech, nanotech, genetech and everything else.
I would implement classes for MF that would deal with this stuff. The Machinist would not only be able to construct and repair weapons, armor and vehicles, but also be able to create and use cyberware. The Alchemist's doings would result in mutants, near-superhero powers and gene-splicing. The Warlock (name pending) would be able to manipulate ambient nanomachinery and energy to do as they please. Finally, the Survivor (name also pending) would not specifically be a tech specialist, but would be a 'heroic normal' who has a wide variety of skills to survive the dangerous world.
It's basically the classic four classes: the Machinist is kind of a rogue, mostly due to their ability to alter machines and such; the Alchemist is kind of a cleric; the Warlock is kind of a magic-user; and the Survivor is kind of a fighter.
The issue here would be basically how to do the magic. The biggest concern I have is with the Warlock; should their powers just be existing psychic mutations, or should I throw in a basic (perhaps Vancian) magic system? And how does the Alchemist do what he does; personally, I kind of like the idea of having materials to make the mixtures, but what is the mixture list? I think there is merit of looking at Labyrinth Lord and stealing some ideas from there
For races I'd leave them as-is, but I would rebrand the Mutant as something like a 'Deviant'. I'd also add in some 'stabilized' strains for quick play, and maybe even extend the definition to aliens.
I'd also want to normalize some things. For example, being 1000 years after the fall, a lot of prejudices between races would have been reduced. I'd also think the particularly bad mutations have been erased or reduced, especially as the Alchemists became more knowledgable. I may also experiment with transhuman body-swapping, but that's just speculation as of now. I think an easy fix would to reflavor the inheritance rule as being a body swap.
I plan on doing a very simple skill system, kind of ripping from Numenera or 13th Age. There will be no defined skill list, but probably backgrounds you make up. If you can apply a background to a attribute check, you get a bonus. Easy peasy.
Though society has advanced, there is still no super reliable way to make guns or anything like that, aside from the creations that Machinists and Alchemists can make. They are basically operating under what could be called 'cookbook science'; they slap together all the bits and pieces, not really knowing all the interactions of what they are doing, and when the finish they having a working gun/serum/etc. That said, I believe gunpowder weapons are a common sight; you will see the occasional laser pistol slapped to an adventurer's side, or a city's guard being equipped with sleek power armor and plasma rifles, but it's rare.
Cities and Wilderness
Cities will not be hunks of scrap metal; they would be gleaming towers of innovation that are maintained by the secretive Machinists, who hoard their knowledge very much like the Machine-Priests of Warhammer 40k. Still, the wilderness in-between is dangerous and is where the dregs of society, 'magic' and unstable tech live.
Expanding the setting will help even more adventuring wise; abandoned space ports, interdimensional research facilities, crashed space vessels and so on. It'd also allow for more enemies besides mutants and robots, bringing in aliens and interdimensional creatures.
So yes, it's kind of like Numenera, but not. In this setting, society has figured out a lot of basics of the old world, and even some major metropoli exist in a state above the 21st century, tech wise. Still, people are operating on a lot of blind faith and the aforementioned cookbook science.
It's Evangelion (I also want to throw in mechs, I forgot), Final Fantasy, Phantasy Star and more all wrapped up, tight, and easy to play. Honestly, the biggest hurdles for this setting are figuring out how to make classes work for MF, which I've seen many unsuccessful attempts of. I think I may go for three abilities per class, but I also need to screw around with Mutant Future progression rules (which I've always hated).
I also want to have a strong theme; I've mentioned Evangelion, and I think it may be interesting to go a Kabbalistic/Goetic/Mysticism route, though simplified and not very preachy (especially since the ideas can get kind of heady).
Regardless, I think there are some good ideas here and I hope you follow along as I develop them