CraftTweaker allows modpacks and servers to customize the game. With CraftTweaker you can change recipes, script events, add new commands and even change item properties!
A mod intended for other mod authors, it contains a revised multiblock API that support multiple client mods without performance penalities, a new new GUI system, a base BlockEntity implementation that simplifiy data syncronization and much more.
Plugin ASM is a lightweight, Mixin-style bytecode injection framework for Paper/Bukkit servers, enabling declarative method modifications via ASM with no manual bytecode writing.