If you are looking for Forge version, it's here! https://www.curseforge.com/minecraft/mc-mods/ftb-gui-library
Common code for all GUI stuff in FTB Mods. Component/layer based GUI creation. Used by mods such as FTB Chunks, FTB Quests, etc.
Example GUIs that are possible with it:
It also adds sidebar buttons that other mods can create with JSON files:
It's not meant to be depended on by non-FTB mods but it's not forbidden. If you lose your mind doing so, that's on you :p