From publisher blurb:
Xanathar’s Lost Notes to Everything Else is a massive collaboration of DMs Guild Adepts that expands the options for players and dungeon masters presented in the D&D core rulebooks and supplements.
This sourcebook provides a plethora of scribbles, scrolls, and schemes curated by Volothamp Geddarm’s protégé, Aladair, pilfered from Xanathar prior to publication of his Guide to Everything. Presented in the crime syndicate’s unique style, including a high fashion collector’s cover, the DMs Guild Adepts bring you new player options, including subclasses for every class, backgrounds, magic items, a race, DM rules options, and an adventure!
Inside this massive tome of full color art, you get:
25 New Subclasses
5 New Backgrounds
6 New Rules Modules for DMs
More than 20 New Magic Items
An Adventure in Chult for Tier 1 Characters