I would like to enable fighters to research new moves in a way similar to wizard researching new spells. Currently, the mechanism of fighter improvement goes through abilities, but I feel like it's limited. You have very specific abilities allowing you "special moves" dealing more damage, but that's basically it.
Ideally the fighter characters should be able to research new, original abilities with the desired effect. Combination of actions with another fighter (such as double assaults) should also be possible.
Does anything like this already exist, or do I have to develop it from scratch? If this were the case, what would you do to keep the game balanced?