I have been trying to come up with a multi-world setting that mixes epic fantasy and science fantasy, and styled like an 80s cartoon (He-Man, Thunder Cats, Heavy Metal, est.), but a little more mature.
In this universe, a great galaxy empire fell, and world, after world is falling to the rule of evil warlords and sorcerer kings. Most of the worlds have fallen to barbarism, and its up to the PCs to stage rebellions, plunder ruins, conquer worlds, and so on. Most of these worlds are as small as moons, but they have earth-like environments (gravity, air-pressure, wildlife, est.). Like Star Wars, it would not be unusual to one or two climates or terrain types. Travel between these worlds are possible through large stargates, built before the fall of the empire. These gates are usually found in cities, and are built, so that airships can move through them. I'm still working on a core setting, as a springboard for further sandbox adventures.
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Another problem, it to what system to use. I'm split between Barbarians of Lemuria and Mini-Six. I might use both. Like like both systems, and they both have their good points. I will post updates, as soon as I come up with more ideas. (WOW, this might have regular updates! Hell is going to freeze-over in a hand basket! ;P)