Avatar: The Last Airbender. If you don't know about it, or you haven't seen it, you really should; it's an epic, imaginative fantasy story masquerading as a kid's cartoon. And I wound up getting involved in a discussion on one fan forum about making a roleplaying game for the setting.
And by "get involved" I mean "stuck my head in and volunteered to do it".
My plan is to adapt the vast majority of the mechanics from d20 Rethought- particularly for figuring out how to handle the system. The number crunching will be simplified, though; among other things, this'll mean using a d10 instead of a d20. Read on for an outline of the various criteria this RPG system will have to meet.
-A focus on characters increasing in power and gaining new abilities (In other words, don't stray from the mainstream here).
-Benders are balanced against non-benders (i.e. Badass Normals).
-Improvisation is encouraged and rewarded, both with mundane actions and bending.
-Bending sub-styles must be done in an open format, i.e. one that lets the players easily come up with balanced crunch to represent their original fluff ideas for something like a style of bending without having to write a page or more of tricky-to-balance crunch.
-Equipment is handled via occasional, unique items/resources (Aang has Appa and his staff, Sokka has his meteor sword and boomerang. . .) and possibly an abstract tracking of resources (so if the party's suddenly stranded the GM has a reference for how much they'd have in the way of supplies).
-Character advancement largely consists of background resources (equipment, connections, allies, etc.), skills, and techniques.
In other words, I want the game's crunch to encourage improvisation and clever use of character abilities, and focus on gaining more cool abilities, without making it so that the key to victory involves alot of number-crunching (during character creation or mid-game). Let's see if I can pull it off!