The Fabric version of this mod has been moved here.
In the lore of Demesne (/dəˈmān/) the Overworld of Minecraftia is crisscrossed with ley lines, flows of magical power. When these lines meet a demesne is formed and the power of the land can be tapped into by building the proper structure on the point of crossing. That energy can then be used to fuel magical machines, rituals and totems.
Here's a video on getting started with the mod:
You can check out the wiki here.