This is a fork of the original Aether II by the Aether team that aims for LTS 1.12.2 support as they no longer support that version.
 

The intention of this fork is to remove the old phosphor version bundled within the mod to provide compatibility with newer forks like Alfheim Lighting Engine, fix any known bugs, and generally smooth out the experience of the mod without changing too many of the currently implemented core features.
 

All of the mechanics and features listed on the original Aether II page are present as is in this fork. In summary, here is a part of the original description:
 

What is the Aether II?

The Aether II is the sequel to the highly popular dimension mod "The Aether", set in a hostile paradise miles up in the clouds, the Aether is an entirely different world from what regular players are used to, filled with fantastic creatures and mysterious structures, the Aether is a world brimming with life and history. You'll have to relearn key ideas as the Aether challenges you with twisted materials, terrifying monsters and deep lore if you want to survive and prosper in this strange new land.