Okay. First time GM or what have you, but I'd like to run this if I still think I have time in a couple of days. I was rewatching some Avatar: the Last Airbender, and a couple ideas I've had bouncing around glommed onto that. Setting would be the 100 years where Aang is missing, so not all the airbenders are dead yet and not all of the Fire Nation agrees with what is going on, which allows players to theoretically be from any nation while keeping avatar shenanigans from violating timeline continuity.
I'm probably going to base any rules I don't mention on a 2d6 RTD format, but that isn't the fun part. Most actions undertaken by players will be in the form of Techniques, which are largely invented by and semi-unique to each player, although teaching/imitation/learning from a scroll will be possible, even if the Technique might change some depending on how a roll goes. To use a Technique, the player spends Chi Points, herein referred to as CP, which regenerate quickly, but not entirely each turn in combat/dangerous situations. Technique costs are highly variable, and most Techniques have a variable into which more CP can be dumped to do something better. Due to the way I thought this out, physics will intrude significantly into the rules, although I haven't figured out a rough estimate on Calories per Chi Point. I should before I run this, though, and that should at least enforce consistent violation of the rules of thermodynamics.
The base Techniques, which every bender will have in some form, are Hold, Push/Pull, and Shape; with the following notes, these are their equations. 1) 'dm' refers to the decimeter (10cm or .1m); 2) 'CP', here, refers to the CP expended on using the Technique; 3) '(x), [y CP]' means that expression x is used for the cost of y CP; 4) '=' means that the preceding variable is defined as equaling the current value of the following expression, even if it includes the preceding variable. Programmers will probably recognize it, although it isn't intentionally formatted for any language I know of.
Hold- Draw H(dm3) of material close and hold it ready where
H1(dm3) = (H0 + CP/(H0 + 1))dm3 or (H0dm3), [2CP], whichever costs less.
Push/Pull- Move P(dm3) of material in three dimensions within a radius of 5m at .5m/s where
P1(dm3) = (H0)dm3, [H0 CP] or (CP/3dm3), situationally.
Shape- Change the shape of S(dm3) of material with 2cm resolution at 1dm3/second where
S1(dm3) = (H0dm3), [2H0CP] or (CP/3dm3), situationally.
Making new techniques from your existing ones is fairly simple, but the first usage costs triple in CP, so it can be no more than 1/3 of a player's maximum power. Then, it can be modified at double cost on the second use or kept the same, and further modified with practice. For an example of how it worked in the show, early in the first season Katara attempted to freeze a soldier, but froze a swath behind her instead. Rather than attempting to do it right, she later turned around and froze the soldier, who was now behind her.
Another semi-unique feature of Chi Points is that they act as extra hit points/armor, meaning that a focused individual is much stronger in a fight, and that taking hits will disrupt your focus and leave you with few Chi Points to retaliate with. This, somewhat unintentionally, mirrors the show in that it is relatively easy to defeat someone without excessive violence, although I don't see any reason to make being hit with a stone cannonball or what have you suddenly nonlethal.
I guess I'll throw some additional ideas here as well, since they aren't well developed enough to each get a paragraph. Non-bending combat will also have a separate Technique tree, likely with the basic ones being Strike, Block, and Dodge, all significantly cheaper than bending in terms of CP. Each turn, players can make up to three actions, two standard (using a Technique or moving) and a reaction, which can also be a Technique or moving, but is triggered by something else, likely an attack, but not necessarily. Hopefully that should get combat more fluid, and allow for interesting combos to occur. I guess that's it, then, so have at you.