I was first thinking of GURPS transhuman space, but GURPS is annoying to anyone who isn't comfortable using a spreadsheet. I could try hacking up some d20 Modern to work with it but that seems like too much work.
So I started thinking of some kind of steampunk D&D-esque world. The World of Warcraft RPG has some rules for an engineer class which on quick scan seems reasonably balanced with other d20 classes.
I'm tired of the standard D&D magic system, so I was thinking of using the D&D psionics rules for the magic system that can be used in a short term, though I was thinking it'd be fun to include a ceremonial magic that is perhaps a bit too inspired by Call of Cthulhu. (Takes a long time to cast, and is mostly useful for summoning things, hopefully binding them, and opening portals to places you really shouldn't go.)
Further running with my basic lazyness I then decided that the core races, Human, Elves, Dwarves, and Orcs were all descended from an original (probably human) race (so you can have half breeds).
One of my issues with the standard D&D world is it made no sense to me for the humans to be in power. So in this game world idea, the Elves are the imperial overlords who've been dominating the region for millennia, and they've outlawed the "sub races" (anyone whose not an elf) from practicing any form of magic. (Not that the other races can't learn/have the right talents, they just get to be hunted if the elves find out about it).
The humans and dwarves have managed to start up a steam powered industrial revolution which deeply annoys the traditionalist elves.
Now I'm trying to decide how science fiction the history should be? Is this a ring world in a far future that's suffered some kind of technology collapse? Were the elves the bioengineered transhumans, and the other races are more closely related to us?