Aether of Night is an unpublished, non-canon cosmere novel. It is also the tenth novel written by Brandon Sanderson. Brandon has no plans to ever publish it, but elements of the magic system in this book have made there way into later books. A draft digital edition is available by asking on his fan forums at https://www.17thshard.com/forums/topic/60219-aether-of-night-manuscript-requests/#comment-585486