A few projects that are pretty widely used in the Melee scene are 20XXTE [0] and Slippi [1].
As far as I know, neither rewrite the core engine of melee, but there are some key modifications like UCF (Universal Controller Fix) in 20XXTE that modifies the way the game interprets analog stick movement to help standardize the effectiveness of gamecube controllers. Without that fix, it's very hit or miss on whether or not certain movement tech would work consistently on a controller due to joystick drift / deadzones.
As far as I know, neither rewrite the core engine of melee, but there are some key modifications like UCF (Universal Controller Fix) in 20XXTE that modifies the way the game interprets analog stick movement to help standardize the effectiveness of gamecube controllers. Without that fix, it's very hit or miss on whether or not certain movement tech would work consistently on a controller due to joystick drift / deadzones.
[0] - https://github.com/dansalvato/20XXTE
[1] - https://github.com/project-slippi/project-slippi